Look at it like this.
Bill is looking for a 2 year contract from another team, hypothetically, and he also wants good money. Let's say he goes to several teams to talk cash.
Well, what will all of those teams want to do? They will probably all want to give him a low salary for his first year, because Kraft is still on the hook for $25M in 2024, so why pay Bill when they can leave Kraft holding the bag?
But if Bill takes a termination payment of, let's say, $10M and then they tear up the deal, he can then go negotiate with other teams and leverage offers from different teams against each other. Teams won't have any incentive to keep his first of 2 years lower because there's no pre-existing deal sending money his way that would offset their payment.
I don't know if this is the situation, but it's what I can see happening. If Bill was simply fired, he could end up going to Atlanta and getting a two year/$31M deal, where his salary in year one is $1M and then in year two is $30M, and Kraft is stuck paying him $24M in 2024. But if he got a lump sum payment of $10M from Kraft to tear up the deal and void the last year, then he can go to Atlanta and get a two year/$60M deal where he is getting $30M each year, plus his $10M from Kraft - meaning he got significantly more money than in the first scenario overall - $55M total vs $70M total.