The set screw style terminals aren't that common here but I've seen the push in terminals on some electronic ballasts and LED drivers. Those generally are designed to only accept #18 solid core wire, typically used in fluorescent fixtures.
On the HID side, some ballasts used Faston quick connects instead of wires crimped to the ballast wire. The oil filled capacitors generally always used Faston quick connects and some dry capacitors are available with them as well.
The lack of terminals was probably a cost savings measure, and also part of the general philosophy for luminaire maintenance here. When the ballasts were in production, they were not designed to be serviced and replaced as the entire "black box" when they were faulty. It made things easier back then but now it also means things like faulty capacitors aren't easy to replace.
The Wago 221 connectors are great for prototypes or for setups that you plan to swap components in frequently. I use the inline version at the lampholders on some of the fluorescent fixtures to make ballast swaps easier.