The way the polls work is that the pollsters call real life people and ask them in real life who they're voting for (or prefer, or what brand of mayonnaise makes the best lube, or whatever else they're polling). They have a list of polls that they've accepted that the candidates have known about for months (Bullock had a complaint about that and the DNC said they'd told them three months earlier which polls were in and which weren't, although they've since struck the Reuters one that didn't offer respondents a list of names to choose from). Enough times, enough people said "Amy Klobuchar" and not enough said "Tulsi Gabbard" that one is in and one is out.
The more important thing is that this whole story is a bunch of Delaney - if you can't clear 2% comfortably by now, you should be dropping out, no matter how much Comrade Carlson and the albino army are on your side.
[edit: Oh, and the other thing about polls vs. online chatter: the polls are only calling US numbers]