A few do. The law requires a break only after 8 hours of driving. With a bottle to pee in and snacks to eat some will do that. Most will take breaks ever hour or two (any who talk to thair doctor will) but those are stop, pee, and get back on the road. They are paid by the mile and long breaks cost money. Team divers only stop for a few hours total per day.

but it will cost the drivers 10k per year - most drivers work for someone else and so won't see a penny of that 250k

Trucks driven by team drivers do. They're used when the load needs to get there fast.

https://ntslogistics.com/glossary/team-driver-transport/

Bladder innovations... an untapped market

I think Coke and Pepsi may already have that market tapped.