The rules are much worse in the states than you endure in Europe. 16 Hour days, up to 8 hours of scheduled block time (can end up be much more with legal to start legal to finish) and minimum rest of 8 hours - doesn't take long for a US regional pilot to be fatigued after flying 5 or more legs that day in some of the most congested airspace in the world.
Glad I moved on from the regionals. The crews are great and I enjoyed the flying but the work rules leave a lot to be desired. As with all things only a disaster that is put entirely on fatigue will cause the FAA to change the rules.