When we bought our last place, I had the keys and our removals van was on the driveway, and they were still packing stuff up.
Our removals guys were getting impatient and started talking about late charges, which helped to hurry them up.
They’d left the place in an absolute state and had to come back the next day to get the last of their stuff, which I’d moved into the garage so it was out of the way.
When my parents moved into their current place, their sellers left loads of stuff that they ran out of time to pack. Never came back for it so my parents “inherited” quite a lot of expensive garden equipment, tools, etc.
My parents have moved 18 times I think, and my wife and I have moved every three years since 2015, so for us it’s a regular occurrence. I guess most people don’t do it as often as us so they aren’t as prepared.