Underhill article: “Saints moves are telling us what they felt the real problem with the team was last season”

Thats a good question. And the answer is to maintain fan optimism (ticket sales) by creating a false sense of hope that “next year is the year” Firing DA and hiring a completely new staff creates provides a sense of hope. But It’s mostly false, because you’re only as good as your roster.
If you recall, Loomis didn't want to. The firing was done at the behest of Mrs. Benson.