It was really only Ole who truly chose to keep picking him. He didn't actually play under Mourinho that often (from memory he only started about 10 league games with a couple of those in the defence when Jose was trying to make a point after not being bought yet another defender), and Rangnick didn't really have any other options. This season he's played decently well so ETH has kept him in the first team for now (helped by Casemiro not getting going yet), but it's very early days. If it's still the same after a few months then that'll be a different story. Personally I doubt it but I'd love for him to prove me wrong by actually playing consistently well.
I'm not sure about the stats this season, but Scott is normally well below average with his pressing and pretty much average with tackles. Being slightly better than Pogba and Matic at those things isn't exactly high praise. That on top of his inability to make himself available to receive the ball and his below average ability when he gets on the ball. He does tend to be good at interceptions as you said though, as well as obviously winning aerial balls. Those things, along with his shooting and sometimes being able to turn and dribble out of pressure, are the things that he has tended to be fairly good at.
I've had no problem with him being first choice considering the options that we had. We as a team tended to be better with Fred and Scott than with Pogba and/or Matic, so in individual games I've generally felt it was the right decision. The huge issue is that Ole never used the transfer windows to actually improve the options we had in that area, which resulted in Scott continuing to be our best option. Something that ETH obviously highlighted straight away with his focus on signing at least two midfielders. Credit to Scott he's played quite well so far (although some people are definitely exaggerating it), but he did the same under Rangnick and then fell away badly after a month or so. He needs to not only maintain the level that he has shown so far this season, but improve further.