Its a shitty situation, but I guess it basically (and most crudely, but accurately) comes to:
Epic: we want everyone to enjoy our game and play together (because the more people playing together, means more $$$ for us)
Xbox: Right on! (my guess is they probably were being trolled initially by Epic due to the current semi-exclusive PUBG affiliation for the console version, resulting with them being left out of the initial cross-play news for Fortnite. But... they quickly kissed, made up, and now they are just happy to not be the odd man out for the next biggest gaming sensation since Fortnight is starting to eclipse their competition (the "horse" they initially backed), and now they can't afford to not be fully "in" for this game in a gaming landscape where they are starting to look in the face of possibly being third place in a three console race in terms of sales if Nintendo keeps their momentum.. Therefore, our experience needs to be as accommodating to attract as many users as possible to use our ecosystem.)
Meanwhile in PS4 land: Fuck all of you! We are number one and there is more than double of us than Xbox bros, and there is no reason to for us to accommodate them and given them a better experience (by allowing them the opportunity to group up with our larger userbase. There are no shortage of people for PS4 gamers to play with between our audience, PC, and mobile, and our audience NOT currently split between two battle royal games, so our people are arguably more invested and dedicated to THIS game than the other platform users.