I T I
Smash Apprentice
Bair/uar combos and the cape are the major reasons. A technical Mario can Uair fox off the stage and cape his recovery.Fox > Peach.
At Wife and Vidjo's level, this gap shortens, but the further down you go, the more overwhelming the fox player is for peach. Even if you're fast enough to smash DI out of the utilt, Usmash is still too much, especially when you waveshine to Usmash. Fox's aerials are too quick, and he's next to impossible to grab because of the shine. Plus, he can always just land behind you. Priority evens out this match a bit, but fox still has too many options and can act too quick for peach.
Wouldn't most fox players want to fight a peach over a shiek or marth? And explain to me how doc and mario are even with fox. chainthrows aren't enough to even it out, imo.
Of course, that's much easier said than done, and definately doesn't make it any better than even for the Mario/Doc.