Radford, Peters and McNamara have all tried and failed, why will it be different this time?

IMO.
Mental strength is collectively cultivated during pre-season, the likes of Bellamy & Maguire are renowned for their torturous pre- seasons, this creates determination , teamwork, motivation etc.
We didnt have this type of pre season, because simply, we didnt have the necessary support staff.

hopefully this will now change

I agree to an extent but don't think its because we simply didn't have the support staff, think its been a long standing issue even under Radford, then in a laid back weak inexperienced Coach in Hodgson followed by a Coach who seemed to have lost interest and desire and again too laid back.
There has simply being no accountability since the end of 2018 from top to bottom and by the sounds of it, very much sulky attitudes if anyone got told judging by Aydins comments in the HDM today, which just confirms what most of have said for long enough.
It's all been just far too easy and a comfortable environment without consequences or accountability almost as though failure is acceptable. With Cartwright incoming we will hopefully see seismic changes if he is the no nonsense type of guy/Coach he appears & reported to be.

I hope cartwright comes in and belts a couple of them. They'd soon fall in line

It worked for Brian Clough.

they'll all be on social media calling out the toxic working conditions at the club if someone upsets them. No wonder we're in the state we're in. Some of them need to grow a backbone