They aren't stupid. Sensors get hot while they're taking an image, and if you can't dissipate the heat quickly enough you have to limit the exposure time. It's likely that new Fuji sensors just run cooler, so they can increase the time they're active.
Yes. People keep repeating this and while it is a real problem for some designs, most professional cameras allow to bypass it with a remote trigger, often an official one.
Besides people were doing long exposure since like forever with great success. If the sensor overheating was a problem, it would make sense to introduce a hard limit and some cameras have them, but from my experience the likely reasons for the prevalent 30s are: 1/ most people don't do several minute exposures 2/ they need to sell remote triggers to somebody.
30s limit was there even during nineties when you could do hours on film without overheating anything.