If you can convince everyone else at your shop that nobody perceives pizza parties as valuable they’ll stop offering them.
Until then, these sorts of low cost rewards deliver value. Only you can fix this. Only you can ruin pizza parties for everyone.
The reality is that they’d offer nothing given the choice between something real and something like a pizza party.
No number of pizza parties equals an annual bonus that matters. So enjoy the small things. It’s what's available. The rest is between you and whomever authorizes your promotion/bonus budget.