In an official statement, he implies that he's moving on to bigger things, having exhausted what he can achieve through the ballroom dance competition show:
I just want to set the record straight to all of my amazing fans that I will unfortunately not be returning for this season of Dancing with the Stars. I’ve been a pro dancer on the show for about seven years now and am eager to explore other opportunities that have been made possible because of Dancing with the Stars. I'm going to take this time to dive into producing and acting, while fulfilling my sponsorship obligations.
Anecdotally, the other day, I was listening to some older ladies discussing celebrity gossip, and one of them said, without any more specific context, "I heard Derek was dating that one girl. What's her name?"
The response from another lady: "Who's Derek?"
"Julianne Hough's brother!" the first lady answered, as though it had been understood by everyone else.
I hadn't realized Derek Hough was now a mononymous entity. I actually thought maybe she had been referring to an acquaintance named Derek. Silly me.
But it made me pause and consider that, to certain segments of television-viewing America, the recurring professional dancers on Dancing with the Stars are, by now, probably more recognizable than their celebrity partners. In fact, I don't think I even need to qualify it; I'd say the more successful dancers are objectively more famous than the average celebrity contestant. I mean, for such "stars" as Kelly Monaco, Drew Lachey, Gilles Marini, or Melissa Rycroft, getting to be on Dancing with the Stars certainly must have been a bigger deal than whatever they came from; most viewers had probably never heard of any of these people previously. Meanwhile, professionals like Maksim Chmerkovskiy and Derek Hough have gotten to be on multiple seasons of one of the biggest shows on television. So these guys are probably justified in thinking that they should have the star power and name recognition now to go at least as far in showbiz as the no-name actors they meet on Dancing with the Stars. Case in point: Julianne Hough is a bigger star in movies and music now than probably a good half of the contestants in the show's history ever were.
That said, I wouldn't honestly expect Maksim Chmerkovskiy to make it as an actor. I'd wager that, if we ever hear from him again, it will be upon his return to Dancing with the Stars.