They would've had to wait almost an entire decade to put anything in the series out, because last generation was a literal nightmare for Japanese developers. This idea that the entire series should just be frozen in time for ten to thirteen years so that people who are too stubborn to play games in a series they supposedly like is maddening to me.
Again. Dream Drop Distance is not that important. I don't know how many fucking times I have to reiterate this point. The only things you need to know from that game are that Xehanort is alive again and Sora failed the Mark of Mastery exam while Riku passed it. That's literally it.
Birth by Sleep is important, yes, but if you literally can't be arsed to play a SINGLE GAME without a mainline "numbered" title, even in a long, long dead period between mainline releases, when it was ported and released at a discount price on multiple more accessible consoles, you probably don't care that much about the series as a whole.