Yeah, that missing was so weird. But we did get the other content bits, so it's not so bad.
I can only imagine that they're retooling and/or waiting to release Extra Battle mode alongside other stuff. The cinematic story mode wasn't enough to get people excited or satisfy them; neither was the Player vs CPU option. That's left me thinking that modes' reception has scared Capcom away from pushing out slim content releases (or half-baked stuff like "Demonstrations").
They've basically promised non-character content releases for this year with the news hitting in between character releases so maybe Extra Battle resurfaces this year? I hope that there's definitely more coming than that though. Arcade mode, Extra Battle and a retooled Survival mode with more missions/targets would help keep more people engaged.
To go even further: Imagine if Extra Battle mode will ended up being their MKX challenge tower with timely challenges and weird, unique mechanics. And if it did stuff like allow you to play as DLC characters and on DLC stages. I think that kind of thing would be a step in the right direction for keeping casuals and lower level players engaged.