It’s primarily because they go against the basic idea of fan ownership in Germany (50+1) which is deeply rooted in German football. The idea is that the majority ownership stays with the club and so with the fans and the community and can’t be bought by rich individuals or corporations. RB Leipzig have been restricting any kind of outside influence to their best of their abilities though.
They did also not even exist 10 years ago, so they lack the history aspect too. Red Bull Salzburg being a thing too and both club’s crest looking very similar there’s just this huge connection to the energy drink more than it is to the actual club, which doesn’t go well with older fans or people who are being brought up supporting clubs with deeper connection to their community.