Remember, this whole thing about crypto is largely decentralized, thus, there is no single authoritative body in control of the crypto market. Although there are few centralized platforms among crypto, the market is largely influenced by the efforts and influence of the users of crypto. How well sellers and buyers treat the coins on the market affect the performance of the market.
Normally I would say the market gets controlled where the volume is. So Bitmex and whoever making prices there surely has a lot of impact. The market cap of Tether keeps falling. I think that is a good thing and hope there will be better options to hedge your crypto investment in the future. For example with the offering of products that automatically spread your investment around.