IMO, the issues took root at QB.
In 2020 they still had solid leadership with Cam and they managed to go around .500 despite the fact that he had zero juice. They bounced back in 2021 with Mac Jones, who I imagine Bill thought would be a leader due to what he did in Alabama. A ****y leader, but a leader.
The problem was that after his playoff appearance and substitution Pro Bowl nomination in his rookie season, he got a bit of an ego. Josh McDaniels left, and Bill also assessed that Mac would do better, at least right now, with less on his plate and the center making more decisions for him. Mac got very grumpy about this and *****ed and moaned to Kraft, outside the building, etc.
For Bill to maintain and save his culture, he would have needed to be able to dump Mac. Of course, Kraft did not allow this and instead forced Bill to both keep Mac and also replace the OC with someone who could go back to the setup McDaniels was running (BOB). Of course, that failed in epic fashion because Bill was right about Mac.
I'm not saying Kraft was wrong, because if Bill got his way then that probably means that Patricia was still the OC in 2023, which is also stupid. Too much stubbornness going around in all directions. But Bill being forced to hang onto Mac definitely took the legs out from his culture starting in 2022 and furthering in 2023.
For Mayo to "fix things" he would have needed to re-establish strong veteran leaders, but instead he promoted everyone to "speak their mind" and "use their voice", even rookies who have never done a thing. It's not surprising that that didn't work.