Probably a combination of a few things. The Outfit under Capone was probably too successful for its own good; as prohibition went on after Torrio got out the Outfit became a ludicrously large, wealthy and consequently more visible organization... I imagine Capone just got far more press, for one, that Torrio ever did. He also essentially saw it through to the end (or at least his end), whereas Torrio abdicated.

Secondly Capone just looked the part, which probably resulted in a lot of the press coverage too. He was a big fatso in expensive clothes with a cigar always hanging out of his mouth; it probably sold papers.

But realistically, I think the simple answer is just that Torrio left before the whole thing kind of spun out of control in terms of size, press, etc.