Why don't gas pumps in the US let you indicate how much you want to authorize?

In the US, most gas stations offer pay at the pump. This is very convenient, but there's one drawback. They don't know how much gas you're going to purchase, so they preauthorize a high dollar amount to ensure it's covered. With gas prices rising, this preauth is also rising. It's currently $75-$100 at most gas stations.

This can be problematic if you don't have that much in the account. If you only want $20 in gas, why are stations preauthorizing $100? If you don't have the funds to cover the preauthorization, you have to go in and have a specific dollar amount put on the pump. Why don't they ask at the pump how much you want to authorize?

This also limits who can use pumps that are only pat at the pump, such as Costco and Sam's club.