I find excessive use of the seat belt sign to be the case with USA carriers in general, but if you think UA is bad, then don't fly AA. Their pilots are hyper aggressive in keeping the seat belt sign on. I was on a flight ICN-DFW 2 months ago and the sign was on for all but about 1-2 hours - with very little turbulence.
Most foreign carriers are much better about this, although I too find CA to follow the AA model, with the sign on most of the flight - and ignored by pax.