@BalrogDeMorgoth most likely they were told to finish the manga fast. And if you think about it, they pulled it off pretty well. I mean, it's reasonable to think the timestop dude would've done these events (even though how he would locate the demon group is kinda weird, and how he got yuuko to get transported there too...even if she might've just gone along without asking anything just because she wanted to meet the other hosts) regardless.
and we might get the third event to be the next chapter, but with gigira deciding to stay with yuuko even while being given the choice to switch partners (I mean, what if there's host who want to fight but their partners don't, and viceversa? the third event still happening could help with that, if you want to keep the setting kinda consistent). I'd be a bit cliche'd, but I believe the author, given a few extra pages, could do it well in a single ending chapter.