What incentive do survey companies have to ever actually ask any person any questions?

Just the fact that they need to do enough work that it looks like they did something, enough to satisfy their sponsor. Otherwise whoever paid them could have just paid a random PhD to attach their name to a made up quote entirely, and we aren't quite that far gone yet most of the time.

And a lot of the time these things are being done by grad students or research assistants, so there is a grade being held over their heads to at least conduct something.

You are right about the rest though, no one reads past the headline and the chart. Because if they did it would be comically obvious how weak 90% of these are in telling you anything.