Update on all of this. I didn't catch this before but just recently came across it. Source here: https://www.gog.com/forum/unreal_series/epic_to_turn_off_online_servers_and_services_for_games_including_ut_games/post26
From user EnforcerSentintel on the GOG Forums:
QuoteHey,
To keep you guys in the loop, there's a bit more to this story than previously known. Epic removing the Unreal franchise from storefronts is in connection with them recently being sued half a billion by the FTC.
While Epic are totally guilty in this case of lining Fortnite with 'dark pattern' psychologies throughout the microtransaction system in Fortnite which mostly exploit (but not limited to) younger users, the FTC is also guilty too of driving the Unreal franchise off of storefronts.
As part of the FTC's punishment towards Epic, the FTC basically (in a heavy handed and non legal way) invoked COPPA, and are now claiming that "Just because a game is labelled as mature or has a mature age rating, does not prevent underage users from playing it", meaning the FTC are threatening Epic that an age rating is not enough anymore, and give or take threatened them to either add COPPA compliant overarching parental controls to these titles or remove them from being sold.
Over the past week or so, OldUnreal are trying to work something out with Epic in order to get the franchise back on storefronts in some way, Epic are on Christmas holiday for a while though and the community liaison will be back in a few days, but Epic are regardless keeping their lines of communication open with us.
So it looks like this might not actually be permanent. At least, the delisting part.