They didn't do so because the White House told them to.
They also only did so for ~24h during which Fox News didn't even run the story because even they thought it might be fake. Which is less of a stance than twitter took. Twitter just disallowed pointing links to the NYPost article for 24h but you were free to talk about the content on twitter.
It's have no problem with Trump getting the actual "pee tape" scrubbed. I definitely have a problem of discussion of it is scrubbed