Because they have an obligation to protect their copyrighted materials and IP.
It was a dieing girls last wish. Telling her family the movie website that already has multiple copies of “UP” certainly would not have hurt the company. Protecting their IP? Not sure how sending them to a site that has nothing to do with the studio, that already has multiple copies of the movie, will hurt their IP.
I understand the studio wanting to protect its copyrights, but cmon...the girl is going to die any moment and them the site that millions of people already know about?