When did the 24/48 hr parking to sleep/ stay over in the parking lot stop? And if anyone also knows, why? What was that policy made for originally?? Is it illegal to do so now??

Actually it is up to the store manager. I know this by trial and error. If you go in and ask to stay overnight they usually will let you. But never assume it's ok. If they do just make sure to purchase any needed supplies there as a courtesy. Also if you are told by the manager it's ok, get his name and phone number so you can put it on a sheet of paper on you dash or somewhere highly visible so anyone who comes to check can see it.

It stop the same time they stopped being a 24hr store (about 2-3yrs ago). You can try but they'll stick a notice on your vehicle that warns you they'll tow you. It's not illegal cause technically it is private property.