Because in every other appearance of Yen Cid and his Tower post-KHII, TT has had zero relevancy to the rest of the larger plot, so there was no need to bring it back along with the Tower. Now, we're seeing footage of both TT and the Tower, so I went out on a hunch and assumed both would be bundled together like in KHII, since both are now relevant to the story.
(Also, to put a finer point on it, I just don't want to forgo one of the finite world options for nothing more than the 4-5 room Mysterious Tower, which isn't all that mysterious anymore anyway)