It's amazing how this claim is perpetrated simply because Trump doesn't have a lot of support on /r/politics.

I'm a very active College Republican at an Ivy League business school. I specifically do a lot of networking and keep in touch with a lot of political groups both on campus and along the East Coast, mostly bipartisan stuff but many general College Repub/Dems groups at the schools with a bigger presence. Almost none of these people are voting for Trump - seriously. My school has one of the highest conservative populations at all the ivies and within our College Republican group we have less than 25% pledged to vote for him. Now some people may be hiding it, I suspect, due to the general embarrassment of it, or may not want to admit they are voting along family lines. But most conservatives, anecdotally, who know a thing or two about politics more than the casual pop-browse won't touch the guy with a ten-foot pole, and that's before getting into all of the sociopolitical issues. I also do not know a single College Republicans group at a school where I would consider the presence of the group "noteworthy" that announced an official endorsement for him, and that's before any of the recent allegations that would make such an endorsement even more passe on generally liberal college campuses.

When you see /r/politics, while the readership is pretty widespread, the submissions come mostly from the kind of college aged, politically interested users likely involved in some sort of political activism with some degree of knowledge. Among that group, bipartisan or not I don't think you'll find very many who enjoy endorsing Trump. That is the primary userbase of /r/politics, which is why you won't really find much love for Trump among people who have spent a significant amount of time studying or at the very least having a casual in-depth interest in policy which his campaign can seemingly defy any and all prior logic in. I think that's why he has a huge amount of following from "grassroots" and especially the outsider-knowledgeable user, just like Bernie did, but regardless you will not find many traditional political enthusiasts who would endorse him, regardless of party.