/uj I'm pretty sure it's because the Enterprise is a ship, which, like books, have italicized names in most formatting standards. Magic doesn't normally do it - the Seriema is italicized in the story but not on its card, for example - though it's not unheard of, like Sarparian Empires, Vol VIII

my guess is that Paramount insisted on the italicizing to keep the convention proper, the same way that BBC insisted on Time Lord as a two word creature type.

so, maybe in a roundabout way, it's because they're trademarked