Why can't they just roll this into the main price of parking?

Be careful what you ask for. A common ploy for dominating marketplaces (Amazon, Doordash, etc) is to prohibit merchants from offering lower direct prices than what's offered on their platforms. They always say this is to guarantee that you'll get the best prices with them. But that's a twisted way of saying all prices must be at least as high as theirs, and the point, of course, is to remove any incentive for merchants not to use the middleman.

Then wouldn't it make more sense to roll this into the main price so the main price seems higher rather than lower?