I dunno. I feel like The Lego Movie can continue going to different places with sequels instead of Frozen.
It makes sense, though. Obviously, with no small part probably due to Batman being in that LEGO Dimensions thing, LEGO wants to push the smartmouthed self-idolizing super hero hard. Plus, Batman is always popular so it's a good move to have him start off the series of films every few months. Ninjago was pushed back to fill in the middle gap between Batman and Lego movie 2 to keep the hype train going, I guess.
Warner Bros. Pushes THE LEGO MOVIE 2 Back Almost A Full Year To Winter 2019 Crap. at least we still have LEGO Batman and it doesnt have to compete with Avengers anymore