The reason is that Sony unlike Microsoft, actually went to the developers and asked them what they wanted the most for next gen and SSD was the most requested feature which Sony delivered.
Microsoft on the other hand thought pure power would be enough with some minimal SSD attached and so it’s no surprise that developers are happy with the PS5 because they finally have a console that’ll enable them to do things they’ve always dreamed of but didn’t have the tech which they now do, so of course they’ll be singing the PS5 praises. Microsoft dropped the ball big time here.