Parking lots where I am are about $3 per square foot.

Solar cells are about $9 per square foot.

You are quadrupling the price before you even get into having to add the frames to elevate them above the 14' minimum clearance, bury all the additional cabling and infrastructure or deal with all the additional permitting and regulatory compliance not to mention liability of you previously open lot now being a code compliant structure.

After that you also have all the headache of actually plugging the cells into something productive.

Industrial power like you would find in a large grocery store makes it nearly impossible to simply backfeed like you would residential solar so you would either need an independent system that used it for something like charging batteries that can later be used for something or a second utility service specifically for the solar to dump it's excess. If you go the second route and you have a decent sized parking lot that is going to require a dedicated run to a substation in some cases because the local distribution lines aren't sized for that kind of local load.

If the cells are doing something productive they will also require maintenance far more than a parking lot that you can safely ignore for a decade or two at a time.

It will also make things in property management like snow removal far more time consuming and risky so therefore more expensive as well while adding additional pest control requirements for all the critters that will try and get into these structures and providing far more surface area for your vandalism cleanup folks to deal with.

All of these costs will be passed directly to shoppers and anyone using the utility.