"Too much food" is a much less fun-killing failure mode than "Not enough food".
You'd like guests to have a decent choice of things to eat even at the start when not so much has been brought and at the end when lots has been eaten. In particular, plenty of choice at the end of the party => lots of food left over.
At least some party food keeps well and serves nicely as snack food, so if you have too much you just eat it later. (Or maybe bring it to another party. Check those best-before dates!)
Having too much food kinda suggests "this person has lots of generous friends and/or limitless resources" whereas having too little kinda suggests "this person has no generous friends and is in financial trouble". Which message would you rather be sending to your party guests?
The wastage isn't super-expensive anyway. What fraction of your income do you spend on party food?
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