Most stalls are bolted together pieces of cheap metal with the most basic latch you can imagine. If an indicator adds 10 cents to the cost it’s not going to happen.
The US is cheap. We even famously have large gaps between the door/stall panels. I can only imagine it is to accommodate temperature/humidity changes so that they don't jam.
Nicer places sometimes have actual deadbolt locks connected to a vacant/occupied indicator on the exterior. But it is rare. Usually it's just a gapped stall with a sliding lock that will often not even line up correctly without wiggling the door.
In some instances I have had to use my gym key fob in place of the missing sliding mechanism to secure the door.
It's to shame you out of doing drugs and having sex in the stalls. It doesn't work because people who are going to do that in a public toilet are usually immune to said shame.
Never seen one in the US. Also in the US, 10% or so don’t even close right. Plus a 30 cm gap on the bottom and a half cm gap on both sides of the door.
It’s only an illusion of privacy; anyone can look through the door or under the stall.