That and UFC matchmaker Joe Silva really wanted him on the roster.
This according to Dana White, who told reporters (via USA Today) the post-fight brawl at Strikeforce: "Nashville," involving none other than UFC 129 main eventer Jake Shields, was directly responsible for Miller's return.
Mayhem, he's banished from CBS for life. ... I think Mayhem was put in a bad position. And I don't know -- I haven't talked to Mayhem about this; this is just what I believe, in conversations I've had with Joe Silva. ... I don't blame Mayhem for the whole situation. Joe wanted him, so he got in here. Mayhem Miller had a contract with those guys. He wasn't being fought because he couldn't fight on Showtime, he couldn't fight on CBS, so he was in a bad position. So that's why that happened."
After the Zuffa buyout of Strikeforce, "Mayhem" became the first fighter to cross over, initially thought to be a product of his contract simply expiring before it was renewed.
However, that's apparently not the case, as CBS didn't want him fighting on their network and that extended to Showtime. It should be noted, no other fighter faced such consequences after the brawl.