Participating in a Ponzi scheme can be profitable if you get out early enough, perhaps people are expecting Tether to stand a bit longer.

Alternatively, perhaps people expect the revelation that Tether isn't fully backed to proceed like the dollar going of the gold standard. It comes with a lot of noise, but the thing keeps working because people keep using it. In this scenario, Tether essentially becomes Bitfinex fiat. That would be a really cool dystopia.