In my previous experience with "shoplight" style fixtures, they were all built to a standard size that allowed a traditional ballast to be installed. I would buy them specifically for the purpose of housing a ballast in my collection. For example, a Lithonia brand shoplight that has had such a transplant now has a permanent home over the barbecue grill. It contains a Universal electromagnetic rapid start F32T8 ballast. Which brings me to the subject of the CCPOC (Cheap Chinese Piece of Crap). This fixture was out in a storage shed. It was of unknown manufacture. When it didn't work, I thought "no problem, I'll just throw one of my many F40T12 RS ballasts in it." The way said piece of crap was designed, the ballast channel is too shallow to accommodate a traditional magnetic ballast. Also, there is only one bolt hole in the channel. All shoplights I've encountered before this had the extra hole to accommodate the longer high power factor ballast. I would've had to drill a hole in the sheet metal to put the mounting bolt back in. Due to the shallow channel, the ballast was too tall to put the cover/reflector back on. One of the new F40T12 electronic ballasts would fit height wise but I would still have to drill the hole to properly mount it. And I'm not willing to spend $20+ to repair a fixture that probably cost half that. This was designed to be thrown away when it crapped out.  

My Hyundai 21W T5 fixture in my room at my new hostel, is the same. Its ballast isn't built in, and is in a separate part in the fixture. But that part is too small for most quality electronic ballasts, which are much larger and longer.

I remember a desk lamp that used 13w pl style CFL lamps. Its ballast (preheat choke) was in a "wall wart" style housing

From my experience its the opposite, most cheap shoplights are never designed for a conventional ballast and therefore will not accommodate one. The most notable are the LOA shoplights which have no ballast channel at all, rather the ballast is mounted in the endcaps with the lampholders. The really cheap Lithonia F32T8 shoplights have a similar arrangement, with no ballast channel and a small box located near the endcaps for the ballast. I have a really interesting unbranded chinese shoplight where the entire fixture is riveted together, not a single screw. After drilling out the rivets I found the ballast inside to be a bare PCB wrapped in yellow transformer tape and just hot glued to a random spot inside the housing.

How do some of these even pass UL inspection? A bare circuit board wrapped in tape and hot-glued to the sheet metal? That does not sound safe at all. some of the connection points on that board are carrying 120v. Electrocution waiting to happen.
I remember the LOA shoplights well. Also qualify for CCPOC status. Typical failure mode for these, one lamp would cease to light, followed shortly thereafter by the other one. Had six in a garage. All of them failed after about a month. Replaced them with traditional F40T12 fixtures. I have long since moved from that house, but those fixtures are probably still working.

How do some of these even pass UL inspection? A bare circuit board wrapped in tape and hot-glued to the sheet metal? That does not sound safe at all. some of the connection points on that board are carrying 120v.

Safety wise ALL of the internal connections "are carrying 120V", like any other ballast.

From the safety standard perspective the sheet meal is supposed to be grounded. So the fixture is a Class I device (metal part protected by interconnection/grounding), so only a "working" class insulation is sufficient against live parts (those connected to the power input). And there the sticky tape is good enough, if it is sufficiently robust against heat and flame. The most frequently used Kapton tape is with great margin.

Don't be fooled, the internals of the "US classic" potted ballasts are insulated from the pot just by a thin sheet of paper - in my eyes way worse method than the Kapton tape (the Kapton tape does not get conductive when wet, way more robust against some edge cutting through).
The only difference: In the old ballasts tat awful insulation is not exposed to your eyes, while here you see it directly, that is all.

If the present construction is less reliable because way more fragile (as it is not that well mechanically protected) is of not a safety problem, but a functional reliability problem (and way less severe than e.g. the missing an/or ineffective lamp EOL protection), so UL don't care.

Top: CCPOC ballast that came out of the fixture.
Bottom: Universal Thermomatic X ballast made in 1980 that works perfectly. Will not fit because it is too tall.

I thought that name was familiar! @Bamaslamma1003, long time no see! I remember your YouTube videos. I discovered HPF Trigger Start ballasts because of you, back when you uploaded a video of the Robertson HPF 2 lamp Trigger Start ballast you had. I've bought many Trigger Start and even Rapid Start ballasts for smaller lamps here recently, and over the past couple years since then.
But yeah, back to the subject... I've had the issue you're talking about on this thread, with the Robertson HPF 2 lamp ballast I bought
not too long after watching your video. I wasn't able to do anything with my fixture... the manufacturers purposefully made the fixture too
small to fit magnetic ballasts. So I ended up taking it back to the store and buying a fixture from Ebay. I'm not sure there's anything you
can do to the fixture to fit that ballast, without potentially damaging the fixture

How do some of these even pass UL inspection?

Not all of them do. The simple solution of a fake UL tag takes care of that!

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As far as fixing the cheap fixture, pick up a cheap electronic ballast for it (keep watch on eBay for that). And don't feel bad about drilling a hole in the ballast channel. Its also very easy to do with that cheap paper-thin metal. LOL

I do remember when even cheap shoplights had holes for the typical cheap LPF ballast they came with, and a standard HPF ballast.

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Oh and like suzukir122 said...
long time no see!

My personal favorite "How did this even get a UL Listing" case study would be those horrible 80s/90s ElectriPak shop lights with the open-coil LPF rapid start ballast (Dim, flickery, LOUD, would cook fast with 34w lamps) zip-tied in.  Fire/electrical shock hazard much? 

I had two of them.  One cooked itself (and smelled horrible) after being plugged in for the first time in 20 years, another had a crimped ballast lead come loose and I chucked it. I did put some LED direct-wire tubes in them and they did make OK crawlspace lights. 

The Lithonia shoplights places like Home Depot and Lowes still sell (Spenards does too, regional Alaska home improvement chain) fit a standard HPF ballast.  They are still T12, apparently still made, and are essentially the guts of one of those horrible Lights of America capacitive-choke abominitions housed in a miniature F-can.  I have a couple and they actually aren't bad in terms of brightness.