I made a comment several years ago where I honestly wondered if there was actually a lack of enough truly good CG artists/companies for all the movies that needed them. I still think that might actually be true. Some of the rebuttals to my theory were that not everyone spent their entire time on one movie, and they could keep hiring more artists, etc. But I still postulate that there are only so many "good" people to go around, and a lot of these studios probably jump at the opportunity to work on a Marvel or Pixar or whatever movie, and eventually someone is going to get the "B team" so to speak. And it seems like, to me at least, that DC constantly ends up with the B team. I mean, do we really think that if Cavill needed his mustache removed in an MCU movie that it would have looked that bad? Sure, you could say that time was the main problem, and maybe it was for the mustache, but as many of us have pointed out, Cyborg looks like absolute shit. Iron Man looked far better a decade earlier, so clearly the tech is there, but maybe the human element is just spread too thin for the industry and they've got people without as much talent or experience working on DC stuff.
I still might be completely wrong, but there is definitely SOME reason that, in general, DC movies look way shittier than MCU movies.