That isn’t true. They were saving for this, but they actually kept their active spending and cash spending up in recent years. It was a function of horrible drafting and losing. They did not have many second contracts to give out and they had to overpay dearly for free agents.
What looked like a massive amount of cap space was due to carryover from many seasons. The Bills looked to have similar cap space this season, but the reality was very different. The Bills has very little carryover. Their space was a function of having had spent up to the cap recently and, after cutting ties with many players and taking a lot of dead money last season, having relatively little cap space dedicated to contracts. It’s the difference between having $60M in the bank and being set to spend $60M less than your budget annually.