There is an T&C agreement between Pinterest and its users. There is no T&Cs agreement between between LAION and Pinterest's users.
Plus, LAION is just an index, whereas Pinterest actually hosts it.
If you'd now go and do the same, create a website that rehosts known content, Google will simply delist you.
But magically, not for Pinterest, they get a boost instead. I've always wondered what kind of under the table deal makes this possible.