I think some of these folks are jaded that Bernie didn’t win the presidency. And that is completely understandable, it’s a shame that our country, and the dems for that matter, are not that left leaning.
But what I think they fail to remember is that Bernie was elected as a Senator from Vermont. Kucinich, Omar, AOC have been voted in multiple times as representatives. While the country as a whole is not so left leaning, there are pockets in this country that are. Change can start at the local level, with actual local laws that impact your actual life a whole lot more than the small, but significant handful of things at the federal level.
But notice that these folks are all democrats. If you want the AOCs and Omars of the world to have more power, then the best way to do that is to vote their party in as well.