In addition to what others have said, parking lots are also an easy and cheap way to keep vacant land for speculative purposes.
Basically, our current property tax system allows you to buy a vacant lot, sit on it for a number of years while paying pennies in taxes (because a vacant lot or a parking lot is very low value, even if the land is very high value), and then resell for a much higher price after the city has grown around it. Basically no work, but tons of free profit.
The remedy? Tax land instead. That way, your tax burden is based on the value of your land, not the value of your improvements, so that this form of land speculation becomes uneconomical, while also strongly incentivizing you to develop something more valuable, e.g., housing, offices, etc.
There is a guy near where I live that I think does this. One of the lots has a tiny restaurant on it that I’m like 95% sure is a front, with a huge parking lot. They’ve bought a few lots nearby and do by the month parking permits. The whole area is being turned into apartments so it feels like he’s just sitting on them for the right offer.