1. Stores that offer free parking have more customers 2. Stores that have more customers can offer better prices to all their customers (including poor people) due to greater sales volumes
Each space requires land, and in urban areas land is not cheap. Even worse, it's land that could be used for more retail, office, housing, etc.
I'm on mobile and don't have access to links, but IIRC each space costs like $10K to provide.
In many cities parking minimum laws stiffle growth by making new buildings impossible to build as the parking requirements are quite onerous. It's either get much bigger scale (also illegal) or get a waiver for parking (difficult for small scale property owners to navigate).
We're not even talking about environmental effects.
Honestly, if parking is so great and rational, why do we have laws requiring X spaces per Y square feet per Z use?