Murray needs someone who will stand up to him and when he barks at them....they can bark right back. Lendl was one. Don't know who else.
I think he did that out of respect. His problem is, he doesn't respect anyone else: not his friends, or his mother, or BG. He's just going to bark at the next person when he starts to struggle. That, or he's lost motivation. Maybe he's realized that being the first Brit to win something in +70 years is worth more than he expected and he's satisfied. In any event, I don't see him doing well for a while.