why can't invite friends to play together the new event?

Hi!
I've seen people talking about this in other places, and when I logged into the game, I found out it was true!

When I tried to invite my boo to play with me, the invite button was grayed out, and I couldn't click it.

Since then, I've been wondering—why can't we play together in the new event? Maybe in a party or something like that?
Or at least invite our own friends?

Hope they fix this before the event ends!