When I was a kid, a normal-sized American adult could open up a bed-width toolbox, look down inside of it, and easily remove a few bags of groceries before re-closing the lid -- all while standing flat-footed on the ground beside their normal-sized American truck.
Things are not that way anymore; trucks got bigger.
The top of the bed rail of an F150 Lightning is around chin height for a lot of folks: https://imgur.com/ZBOBqJc
Oh, I was a smaller kid back then and I guess I wouldn’t find it very accessible either way. Also my dad was tall. Coolers fit in the back also if you want to use those instead.
Things are not that way anymore; trucks got bigger.
The top of the bed rail of an F150 Lightning is around chin height for a lot of folks: https://imgur.com/ZBOBqJc