A stoplight is not just for some of the road users.
And the others can blow through without a care in the world... cars won't hit them will they?
Unfortunately many are poorly designed for bikes. Which Paris is apparently realizing and trying to fix, at least in a few situations.
Lights are also a bit odd... even when driving a car, it is not uncommon to get stuck sitting at a light with no traffic, especially when driving after midnight. For the night traffic, some cities are actually setting their lights on blink to help with the problem of sitting at lights with no traffic. Some places probably only need the lights a few hours a day during rush hour.
I do find it interesting riding on bike paths with no stop signs or yield signs at path/path intersections. I assume some collisions occur, but they seem to be fairly rare. The cyclists and pedestrians just seem to work it out.