This 'reason' doesn't even make sense. Whatever the best platform is, it can still allow cross platform play. I just don't see how one leads to the other.

Isn't the real reason that they want all the people who play Fortnite on PS4 to tell their friends who are looking to get a console, "make sure you get a PS4 so we can play Fortnite together."?

I don't play Fortnite so I didn't really appreciate how big a deal this is but I was talking to some people in my extended family a few weeks ago and they were talking about Fornite and between all of them they played together using Switch, Xbox, and PC.

I think this is really bad for Sony it hurts their reputation with me a lot even though I don't even care about Fortnite. I just can't think of a non jerkish reason for them to have this policy. I remember when Sony came out with videos making fun of Microsoft after Microsoft first announced the Xbox One like "How you share games with your friends on PS4", where they were making fun of Xbox. It would be funny to see videos now from Microsoft about how you play Fortnite with your friends on Xbox One and it shows them playing with people on a lot of different systems.