There's a fraction of Big 4/MBB associates who dream of becoming partners and this is the hazing ritual the culture has established to select who will get to stop 3-4-5 / 80 hr work weeks and pivot into something a little less insane with more money. The problem is: there aren't that many positions for project leaders through director compared to the number of associates. They'd probably be better off winning the lottery or going to work for one of their clients so they can have a life now rather than the nebulous promise of one at some point in the future.