It was always mentioned here and even discusses several times already. There are even sites before that were caught not being fair.
Personally, for me, I'm not verifying the fairness but just putting the trust in that site not to cheat on their players.
most casinos are indeed explaining the provably fairness on their site as they allot a certain space for this. some actually have tabs where you can check the fairness of their system. but just like what you said, not many players are checking the provable fairness if they know they are playing on a reputable site. but for some new casinos and their launch is quite a controversial or doubtful one, some are really checking their provable fairness system.
there are several threads here also discussing the provable fairness and how to test it.
Do you verify every bet as a gambler? Provably Fair Guide.
The Fundamental Flaws Of Provably Fair