And currently bitcoin’s in an unusually large bubble, so there are lots of people buying into it who’ve never previously had experience of it. I see ads for, basically, “get rich quick with bitcoin” every day now. The people clicking those are not the world’s greatest critical thinkers; if the site on the other end says “buy tethers with our affiliate code to BUY BITCOINS AND GET RICH”, they’ll do it.
There are sufficient people buying tethers at face value, from the company, to keep parity. And I don’t think there’s really a facility to short sell them (that might change things a bit)