They systematically violated copyright when they grabbed whole internet to train their models. Do you really believe that they will stop stealing because they signed some funny ToS? Especially when every bit of data they have and competition does not have is making their model better.
Blame copyright law. AI training is very comparable to compiling an inverted index, which is considered transformational even though you can recover the input documents from an inverted index.
People downvote you like you're being paranoid, but we're literally discussing this in a thread that shows how little respect those companies have for any sort of trade secrets.
There's an important difference between "knowing" and "believing".