Probably the way the whole writers strike thing went down at DWTS and them deciding not to honor the writers union and the other actors not honoring the writers union and take a pause just soured their relationships. Matt is a WGA writer too, as well as a SAG actor. The ONLY reason Matt performed last night was because an agreement was reached for the writers in time. So, he had already had a foot out the door.
If the writers strike was still ongoing, probably the show would have just pretended he was never a contestant, instead of doing one show and having him "eliminated" immediately. And probably no one got to vote for Matt, regardless of which platform one watched on. The show probably ended voting way early so that they could later purposely show he just didn't have enough votes even if he had wanted to stay.