If RV parks would offer those who choose just a place to park, no hookups for overnight at a reasonable cost perhaps people would choose that instead of Walmart. Many parks have priced themselves out of the price range of travelers/overnight guests. I don't know what the solution is, but many cannot afford to spend $100 on a couple of overnight stops before they even arrive at their vacation destination.
We have never parked in a parking lot, but go to rv parks and campgrounds even if for just 1 night. I do understand the convenience of just being able to pull off the highway into a parking lot, sleep a few hours and get right back on and continue on your way. That is not how we travel even though many do.