In Mario Kart every player gets access to items just by driving, and most of the powerful ones do all the work (driving for you, aiming automatically etc)
In Smash the better player can monopolize the items, and is better able to use them.
Maybe the next Smash should find a way to change that - give everyone items, better ones to the losing players, and a make them a bit more foolproof. Could actually make casual play a lot more fun.