You still need to sort out and sign a bunch of identity confirmation/anti money laundering stuff. The government has a good track on you, at that point. It’s far from perfect, but stops people getting it signed off by a random friend, that the government has no clue about, and might not even exist.
I suspect it’s a selection effect. Amazon is a pain in the arse to work for. Decent drivers are in demand. This makes it easy for good drivers to jump ship to other companies. This leaves the inexperienced or just stupid drivers left to deal with the BS.
If you’ve not driven a van before, they are intimidating to maneuver, at first. It’s takes time and skill to spin them on a dime, and slot them in, with awareness of how much space you are leaving. Novice drivers simply lack that skill.