Bonuses started after delta bought them in BK to provide a lower bid as companies like Skywest had a clause requiring them to be the second cheapest delta feed, considering gojet got delta planes to be one of the cheapest another like endeavor would really force companies to be cheaper, problem is no one would come to a bankrupt Airline so they had to offer bonuses and make it for a number of years to incentivize people especially military who didn't care about upgrade.
Endeavor is not around to be deltas only feed, at most they were purchased to provide lift ar the regional level that delta can control should other lift providers go under, which is not happening yet.