3rd party exclusivity is bad for everyone involved.
Some gamers get excluded from playing a game they might want to play.
Only option would be to buy all the systems.
3rd party developers are losing tons of money by disregarding potential customers on other platforms.
Fanbase cannot evolve further, which will hurt potential sales of every sequel.
Leaving out a single platform could be beneficial for a developer, but making it exclusive for one definitely isn't.