TTC has such an iron grip on Tetris that even clones which don't use the name or anything similar to it are still at risk of being shut down, it's ridiculous. It's possibly the only example of game mechanics being de-facto copyrighted, in spite of game mechanics ostensibly not being copyrightable, due to some legal sleight of hand where they successfully argued that the look of Tetris is their exclusive trade dress. That look is inextricably tied to the mechanics, there's no way to make a Tetris clone which doesn't look like Tetris.
TTC exists solely to collect rent on Tetris so they're never going to let it slip away if they can help it.
If we lived in a just world, that would make the look uncopyrightable, rather than making the mechanics copyrightable.
TTC protection is based around other IP constructs. Here's a good sample link from a source that seems to know what is up, which I link to for the legal analysis rather than the details of a 2009 court case: https://www.gamedeveloper.com/game-platforms/exclusive-i-tet...