I imagine they throw the van into any space they can as they aren't paid enough. I've seen a local Amazon delivery driver running back and forth all day long. It can't be worth doing that.
"I need this job and they don't give me the logistics to park appropriately, so I do whatever I can, knowing I'm not doing the best societal thing with where I park. I hope I'm not late on rent this month."
"I'm underpaid and have a brutal schedule so I'll take all the shortcuts". Hence their 'dump and run' delivery style. Also the large quantity of piss bottles on the roads to their depots. I can't really be annoyed with the drivers when Amazon's system squeeze every drop of work out of their drivers and warehouse staff. But, ultimately, we're to blame because we want free delivery for all the rubbish 'we' order online.