When you go to withdraw from Tethers it basically says "if you don't have more than $50k in claims, go away" [1]. Suffice it to say that most of their customers don't have that.
My guess is that Bitfinex, through a combination of wash trading and Tethers, have been pushing up the price of Bitcoin and they've basically been running a Ponzi scheme.
[0] https://tether.to/wp-content/uploads/2017/09/Final-Tether-Co... -- "This engagement does not comtemplate tests of accounting records or the performance of other procedures performed in an audit or attest engagement"
[1] https://cdn-images-1.medium.com/max/800/1*7BOwdYvUycjNFdUB2e...