I'm not defending Wal-Mart, they do some silly things sometimes. If Sam Walton could see what its become, he'd shoot half his family. Not that he had anything against making money. One of the shrewdest businessmen I ever saw. Anyway, I digress.
Wal-Mart has all those locked up items for a reason. They've been sued too many times for trying to catch wiley shoplifters. It's gone beyond stealing some high priced stuff. They've learned what the stores can and can't do to catch them, and they set up the loss prevention people. As a result, Wal Mart can't stop people they suspect of shoplifting anymore. Unless a member of the store's management team personally sees the person stealing, and they cant lose sight of them for even a second or its called off. Too easy for the would-be thief to dump what they pocketed and pretend they never had it. The safest way they could come up with to cut down on the thefts while protecting themselves from lawsuits was to either move the more expensive small stuff to the front, and you pay for it when you leave, or they make you pay for it at the counter in that dept. Inconvenient? You bet, but blame the crooks, not the store.
As for the cameras in the parking lot, they have nothing to do with you. Wal Mart never had outside cameras until the mid 90s when one of their store managers was killed by some men who waited out in the parking lot for him to leave for the night. They pulled guns on him, forced him to open the doors and take them inside, and to open the safe in the store. Then they shot him and left him for the morning crew to find. All Wal Mart employees are now covered by cameras, and no one walks out to their car alone at night. Not even the boss. If the Manager is the last one there to leave, an overnight janitor is on duty and stands at the door until the last person is in their car and gone. Before that time comes, that person will have gone outside and moved their car close to the doors, with someone else watching. Those cameras have everything to do with keeping their employees safe, and nothing to do with watching you.