Honestly I think part of it might be that Musk, in a way, represents an (almost) naive hope ("let's go to mars!"), and as far as I can tell the alt-right mostly runs on cynicism and criticism.
I find it hard to properly argue this, because it's based on mostly a feeling I get from following /r/the_donald and various other alt-right(-ish) sources.
But the best way I can explain it is how I feel when I watch Fight Club, in particular the scene where Jared Leto gets beaten to a bloody pulp, and the main character says that he just 'wanted to destroy something beautiful'. I remember that the first time I watched the movie as an angsty teenager, this scene gave me a (thankfully) fleeting feeling of power, anger, mixed with disgust and self-loathing.
Interestingly enough, a game like Bioshock had a similar effect. The message is clearly that the 'Randian' approach leads to all sorts of horror, but for some reason there's also something appealing about the situation, at least to the person that I am (and I can easily see a version of myself in a parallel universe being part of the alt-right).
Anyways, my point is that anything that has a whiff of naiveté, grand hopes, and the kind of 'moonshot' idea that could possibly lead to utter failure, all of that is antithetical to the general alt-right perspective.
At the risk of shoe-horning an author I like into this, I nonetheless feel that David Foster Wallace somehow is able to capture some of this.
> “So far it seems as if people think it really is sort of a book about drug addiction and recovery and, you know, intentional fallacies notwithstanding, what was really going on in my head was something more general like what you were talking about before, that there is a kind — that some of the sadness that it seems to me kind of infuses the culture right now has to do with this loss of purpose or organizing principles, something you’re willing to give yourself away to, basically. And that the addictive impulse, which is very much kind of in the cultural air right now, is interesting and powerful only because it’s a kind of obvious distortion of kind of a religious impulse or an impulse to be part of something bigger. And, you know, the stuff at the academy is kind of weird because, yeah, it’s very high-tech and it’s very “become technically better so you can achieve x, y, and z,” but also the guy who essentially runs the academy now is a fascist, and, whether it comes out or not, he’s really the only one there who to me is saying anything that’s even remotely non-horrifying, except it is horrifying because he’s a fascist. And part of the whole — part of the stuff that was rattling around in my head when I was doing this is that it seems to me that one of the scary things about sort of the nihilism of contemporary culture is that we’re really setting ourselves up for fascism. Because as we empty more and more kind of values, motivating principles, spiritual principles, almost, out of the culture, we’re creating a hunger that eventually is going to drive us to the sort of state where we may accept fascism just because — you know, the nice thing about fascists is they’ll tell you what to think, they’ll tell you what to do–they’ll tell you what’s important.”
My apologies if this doesn't really add up to anything. The topic just hits a nerve and I'm trying to find a way to properly put it into words.
EDIT: found the full quote