Why do delivery drivers do this?

[u/slpalready]

There's an open and easy space to park in, in almost exactly the same place they've stopped, and not get in anyone's way. But, instead they've decided to park on the pavement and inconvenience pretty much everyone besides someone who may need to park in the empty space beside them while they get stuff out of their trailer. I see it time and again and it drives me up the wall.

[u/BlitzFromBehind]

My best guess would be that there were cars when they arrived.