There is a sizable group of young men who not only feel like the Democrats (and people on the left, in general) have not only ignored the issues they face, but view them as being inherently bad in some way. The alt-right spaces have been very successful at translating discussions of privilege into a message that everyone but the GOP believes young men, especially young, white men, are doing just fine and are greedy for demanding any sort of help or attention, as well as inherently being oppressors of the marginalized groups that have featured so prominently in contemporary discourse, with no way of redeeming themselves short of complete and total submission to these groups. Basically, painting white guilt on steroids as the only acceptable option for these young men to the Democrats, but with the caveat that nothing they do will ever absolve them of the crime of being born with a penis.

This is obviously nonsense, but it's quite attractive to these people to hear someone say that they acknowledge their problems, those problems are real, and what's more, those problems are not their fault. The absence of acknowledgement or inclusion of these problems in the Democratic talking points lends it some credibility, and there's a robust media apparatus in place, with folks like Joe Rogan or Jordan Peterson, that allow them to form some sense of community and identity, while also moving them further on the way to being full-blown MAGA supporters.

It's the same sort of strategic failure that the Dems encountered with working class people more broadly; they dismissed their concerns, told them everything was actually fine, when many acutely feel the struggle of existence, and didn't offer a platform that got them excited and feeling like their economic concerns were being addressed. Then add in policy proposals that specifically target groups like black men, and many of them begin to view the entire field of politics as a zero-sum game, which one side is looking to rig against them.

Of course, this is a misguided take, at best, but it's amplified by podcast bros and alt-right youtubers, and the way the DNC strategists takes the votes of these groups for granted lends further credence to the notion, in their eyes. The DNC desperately needs to come up with some countermeasures for the alt-right media bubble and stop assuming they can count on any votes as safe, especially if they don't have heavy messaging targeting the demographics in question.

More like nagging at them.

Multiple reasons, but it starts with terrible education. They don't know how to verify information at best, and at worst don't want to, they believe they win when they piss off someone they don't like. This means the information they get on current topics is generally something pushed by someone either paying an algorithm to target them or by things like AstroTurfing.

There's a lot of value for the hegemony class in getting people to not care about the climate, endless war, genocide, and human rights in general.

And then you have the out of touch authoritarian liberals/neoliberals that control the liberal side of the mainstream media.

The way I see it is, the youth were super excited about changing the shitty situation that faced them, and the prospect of having Berny Sanders as president, who also wants to change that situation, and they had that ripped away from them, so they were radicalised, they spend 4 years with a senile old man, who did nothings to change the staus quo, and so they voted naively for the candidate who proposed change.