#1 It's not all that certain AI training is fair use. There could be significant damages if it is found to not be fair use.
#2 "We're going to steal your shit even if you won't give us consent to do that" is a bad idea. We're already seeing the practical results: People stop/reduce posting their works to the clearnet. What's your scraper bot going to do? Create an account on every 'private' forum and immediately get sued? Pay a subscription fee to every single Patreon page?
And the big one, #3: It destroys public support for your technology, which is essential if you want to survive the oncoming government regulation.
Look at the public response to various tech companies stopping their AI rollout in europe over EU regulations. Varying from "Yes, this is exactly what we asked for" to "Good fucking riddance".
And it will get only worse yet. Europe's privacy authorities are already issuing quiet statements that the scraping of social media posts, such as is done for AI data collection, is not legal under the GDPR. (The law's pretty clear on this, it doesn't matter that it was "posted publicly", you're not allowed to use personal data like that) There's already whispers of going after the LLMs themselves, as they contain and continue to process personal data as well.
AI needs public support, and the lack of consent is slowly bleeding it dry.