The seat belt sign is turned on by the pilots, not by the cabin crew. Some airlines do leave it on for far too long. Generally US ones, so perhaps that’s something else to blame lawyers for. But, far worse than having in on for too long, is allowing the cabin crew to keep working whilst it is on. That simply leads to ignorant comments about being able to ignore the sign.
I only ever turned it on when I meant it. The cabin crew had one minute after it came on to be seated, and I would be informed by the CSM when they were all strapped in. But, I also knew how to use a radar, so I was generally pretty successful at threading my way through the weather without encountering too many bumps. But, if we got it wrong whilst going through the storms (in particular the stuff around the equator, where the belts can go on for hundreds of miles), then you‘d have zero additional warning. It would be smooth, then smash. But, I guess you can use the radar feed back at the passenger seats to make your own assessment.