Reminds me of this parking ramp I used to use occasionally. I'd park for hours and when leaving the guy in the booth would tell me the charge and it would always be ridiculously low, like $0.50 or $1.00. Definitely not enough to pay for the guy to sit in the booth.
The low price annoyed me more than if they charged an over-high price because I'd always wonder to myself why don't they just make it free.
Perhaps keeping the booth guy employed was the real point.
Are you sure that is the extent of their business? Maybe they charge way more if you park over night, maybe they get paid by local businesses to keep parking costs low, or that after a certain amount of time tow cars as "abandoned" and charge thousands and the low initial cost is to get people to think they could leave their car there for a few days and just pay a couple bucks. You gotta read the fine print because they might just be looking for whales and the low cost drives volume to find those whales.
Making it totally free would invite absolute abuse. A little friction goes a long way.
IIUC, most parking lots are real estate plays -- the real money is in flipping the land; money made from parking tolls is gravy.