It's a chicken and egg problem. "there's never anyone good to vote for", "politicians don't care what we think", etc...

On the other side, politicians are not going to stick their necks out for voters that doesn't show up reliably. Even if they did start showing up in greater numbers, there would be no guarantee how long that would go on for, since you would constantly have new voters coming into that age group. Unless something shifts pretty drastically in party platforms, a democratic candidate already knows they are going to get a good majority of any young voters that do show up. It must make sense to just wait until they get into their 30's and they become more consistent voters before seeing what their priorities are.

You would have to be able to trace any kind of young voter surge back to something that seems fairly reliable, like requiring significantly more civics education. Implementing something like that and seeing the results would easily take a decade or more.