How come stairwell light timers were never used in the USA?They seem like a great idea, but WHY WEREN'T THEY USED IN THE US?So. Confusing.

I assume you mean a timer that turns the stairwell light on long enough to reach the bottom and then turn off. Here in the U.S., our stairwell lights are typically on three-way switches, with one switch at the top and one at the bottom. So you can flip the light on from the top, walk down, and then turn it off with the switch at the bottom. In commercial environments, stairwell lights are usually just left on indefinitely for safety.

Here in Israel, all residential buildings have stairwell lighting timers.

They are used in apartment blocks, where the electricity bill for the common loads (stairs and outdoor lighting, lift, pumps etc) is divided between all apartments, so they are not abused by being left on forever

In some small buildings for like 2..3 families it can indeed be still on 3W/4W switches, and in private homes it is mostly on 3W switches

There is also another system which uses stepper relays, common in public buildings. Same as 3W/4W, it allows manually switching on and off the lighting from a number of locations but does not control how long the lighting is on. The switches are all momentary push buttons wired in parallel, they control a stepper relay, that controls the lights (directly or through a contactor if there is high load)

How come stairwell light timers were never used in the USA?They seem like a great idea, but WHY WEREN'T THEY USED IN THE US?So. Confusing.

I think this flashing thing is really irritating especially when used with PIR sensors. While the savings were worth to bother with high-consuming incandescents, modern LEDs consume just single digit watts and can be left on 24/7.

And I thoroughly hate these abruptly going from dark to full brightness as you move in. A proper implementation is to stay on the standby brightness forever, gradually ramp up as PIR sensor triggers, ant then also slowly turn down on timeout. So easy to do now with LEDs...

Here practically everywhere the timers got replaced by PIR sensors.
The timers had one big limitation: Controlled the whole stairway shaft at once, so always all the lights were turned ON.
Plus with things like floor cleaning the lights permanently shutting down were quite annoying. Yes, the systems usually had a "permanent ON" switch/feature, but first you have to go to a certain floor to activate it, but second you need to go there second time to deactivate it back. So people rather tend to jam matches into the trigger buttons. And often forgotting them there, not only leaving all floors lit permanently, but also frying the timer (as it permanently cycled to reset; at that era most of the timers were of the electropneumatic types, where an electromagned actuated a plunger turning ON the lamps, pressing a spring and arming a vacuum piston timer mechanism; the seal around the piston tend to wear out if left cycling for a long time).

PIR switches turn ON just the lights at the floor where someone actually is and even with the cleaning, they stay ON (or could be activated by just waving a hand, if you happen to work further away from the sensor).
And the problems with matches or similar stuffed to hold some of the buttons permanently ON are gone as well...

Here the timers with button are used to this day, and quite well so. Even in new construction (built right now), buttons for starting the timer on each floor (and in modern buildings with more complex corridors, often a few along the corridor) are standard

In 8+ floor homes for many years (at least since 70s) it was common to split the staircase to 2 sections controlled by separate timers. This both helped save energy, and prevent uncertainty whether the time setting is long enough for anyone to walk though many floors

In some modern homes the sections are smaller, i have seen homes built in the 2010s where 2 floors or a separate corridor in the entrance can have their own separate timer, and in some homes there are in addition few luminaires that are permanently on

Nowadays most such timers are electronic, some (Theben Elpa) electromechanical and are reliable. The most common fault i seen with those is contacts of the relay welded together (so being stuck in lights on position) as result of closing into a short circuit (mostly due to insulation failure in luminaires), very rarely any failures caused by the timer itself

In the old days the timers here were thermal. Button powers a high power heater, heater within 1 sec pushes a rod (that expands from heating) into a microswitch, that switch the light on and the heater off. After a set time (tuned by the initial pressure of the rod towards the microswitch button) it cools down and releases the microswitch. Those were made from the 70's (maybe 60s ?) up to the early 2000's

In the original ones the microswitch body was made of bakelite and they were standing to stuck buttons moderately well (although eventually the heater burns out, but it may take years of abuse before this happens). In later ones the microswitch body was made of plastic. Repeated reheating of the rod eventually conducted enough heat to the microswitch that it melted and seized, usually in the "light on" position

PIR's are not a norm, and if they are installed, it is usually by individual homeowners later on