Because AI wasn’t a big thing before 2020, and no such permission in obtained material has been legally necessary so far (lawsuits are pending of course). If something has no incentive to exist it will not be created. There’s plenty of ethical justifications why no such permission is needed as well.
"But a data source of such size of material where everyone opted in to use for AI explicitly does not exist. "
Dang I wonder why 🤔🤔🤔🤔
Because AI wasn’t a big thing before 2020, and no such permission in obtained material has been legally necessary so far (lawsuits are pending of course). If something has no incentive to exist it will not be created. There’s plenty of ethical justifications why no such permission is needed as well.