If you can compare the code and it matches you probably have a good case if the AI user can't demonstrate it's not coming from you.

There's different kinds of datasets. Some respect, select and disclose licenses, others do not.

Some model trainers use any data they can, others are selective on what they train on.

It can also be a decision on principle rather than current or future enforcability. If you say "don't copy this" and someone blatantly does, the morality is clearer than if you didn't specifically say that.

There's also a question of how court rulings and law may change the situation of enforcability and usage/ignorance risk.

MIT requires attribution too. GPL is, at the very least, a stronger statement of intention and demand. It can also be seen as protest or indication of a broader move of corporate AI exploitation leading to damage to the whole FOSS ecosystem, with additional restrictions being applied. Corps that would use AI now can't use the MIT product anymore like before.