I honestly have no idea why. I have had both the PS5 and XSX since launch (yes, I got very lucky), and I have been a PS fanboy since the original, but the XSX is just way better IMHO. I barely use the PS5 unless it's for exclusives, of which there are very few.
I feel like there is a lot of inertia keeping people with what they know, but if you were to give a PS5 owner an XSX for a month, they'd go, "Oooh, I get it now!" and switch.
At a bare minimum, the XSX is much better for everything besides gaming (streaming, etc), the controller is SIGNIFICANTLY better (subjective, but man...huge difference), Gamepass is way better than PS+, and there are more exclusives on Xbox.
I wish the PS5 were better because I'd rather not support MS. But the gulf is so wide, it's hard to validate buying the PS5 in my mind. There's a reason I have a second XSX while the PS5 is gathering dust until Spider-man 2.