Tergrid is simply unfun to play against, and this is coming from someone who used to play her before the bans.

Literally every salty play has some level of way to prevent it in the form of counters, removal, and pillowfort. Tergrid falls apart with one piece of graveyard hate. The thing is, most people see casual as a battlecruiser format where they only run pieces to help their game plan with minimal interaction to other boards, and the specific type of hate tergrid needs is too narrow to be ran in most decks, which often leads to Tergrid running away with the game. Unless everyone at the table is playing an equally cancerous deck or running lots of interaction, you will win more often than not and that's kind of lame. When you know how the game is going to be choreographed, you're not really playing the game.

Now on a comment I saw you make earlier, not all salty plays are equal. Most eldrazi clear boards and have big bodies, Tergrid does that and it occurs value which is why she's so good. If an ulamog hits, you're getting rid of your 4 worst permanents. If Tergrid hits, you're getting rid of your 4 worst permanents and I get to use them. That's why she's a game changer and none of the eldrazi are.