I don't really understand why they would do such a thing, unless there are regulators behind all this choice for these stablecoins.

It could be a plan to force people who desire to continue to use their stablecoins to move to more centralized protocols, for the sake of keeping control over users and exchanges.
Anyways, as it stands, one can only hope most of users won't fall for this and stay with stablecoins being offered in Ethereum and Tron.

In the end, the direction of Blockchain as a liberating technology depends almost exclusively on all of us...
This is very bad news... Everyone using those two stablecoins should know about this.