Maybe he's outgrowing that initial group of coaches who came with him. Not like he chose any of them for bigger roles...
This is my take. He purposefully brought in mostly well seasoned, experienced coaches to surround himself with initially. I would assume because as a first time HC he felt that was the way to go about it and receive valuable feedback.
McV knows what he wants now, four years into it.
I think this is what is going on.
Think about it... as soon as Mcvay was hired he built an entire staff.
In doing that, his first goal was structural. OC check, DC check, OL coach check....
Sure, he interviewed for culture, but he needed a lot of spots filled. Kept a few carry overs, but had to pick from the available coaches that off-season.
Each year it’s the same assessment, now 4yrs later...
he’s all about culture and fit.