Why switch and not ps4? Their games would be much easier to port over to and gamepass would be much more profitable on the ps4.
Easy: Sony is competing with MS in more markets than simply videogames.So it makes sense to help a company that wont get in the way of their core business like Nintendo, which is purely videogames-related.
But the biggest reason must be because Sony is trying to make their own subscription service to work, which is called PS Now.So allowing MS to put Gamepass on PS dosent make sense for Sony, at least for now.
My (locked) thread about how difficulty should be a decision for the developers, not the gamers.