Unfortunately, if they did that then Pixar would have officially forfeited their copyright rights. Anyone could make a claim on the property then. Pixar would be stupid to have done that.
It's the same thing if I decide I want to print out some Coca-Cola t-shirts for myself. If Coke finds out and they do nothing about it, then they have de facto given up their rights to their trademark. It's just how this stuff works.
the spelling police.
Not really...but some incorrect words are just painful to look at. Dieing is one of those words. Plus since dieing is a real word I figure your browser didn't give you the hint that it was wrong.
You're confusing copyright and trademark. You can lose trademark (Coke T-shirts) due to non-enforcement, but copyright (Up!) remains until it expires even if you don't enforce it equally.