It’s supposed to work both ways - I work 60 hours this week with the implicit understanding that I work 20 next week. Sure, I don’t get OT pay, but I can abide by that as long as it all balances out to 2000 hours at the end of the year.
That said, the abuse of the exemption system is arguably a pandemic in the US.
The problem is that unlike with proper overtime protection, it's just an implicit understanding that is in no way guaranteed.
Overtime laws generally allow taking the hours worked back as PTO. The only thing is that usually there are limits to avoid running everyone ragged with no end.
Of course that only applies to people working on employment contracts, not those who got seduced by "B2B" :|