It seems the logistics issue is pretty simple, from other posts, it appears these companies have drop down options for delivery times on their sites or will give you one if booking on the phone. Each company knows how many units and delivery vehicles they have, it is very simple to figure out how many they can deliver per hour to the various resorts. When one slot fills up, that hour window is removed from the options list and the customer can either choose the next most preferable time or find another supplier that can work with their preferred drop off window.
I think we all get that there may be surge points for when people want drop off/pick up, but every industry has those, if my local AC guy, pest control guy, repair guy, delivery restaurants, and many others can figure out how to make it work, I’m positive these scooter delivery guys can figure it out and provide reasonably reliable estimates and stick to them (obviously unusual circumstances can delay things, but that can happen in literally every other facet of your trip and your life too).
I’m surprised Disney didn’t do this earlier. They shouldn’t have to hire extra staff at every hotel to manage an ECV parking lot/valet service for companies and/or customers who may leave them there all day. Plus, if they are receiving them from multiple companies during a surge check in time, guess what, that’s even more staff that is having to go deal with deliveries instead of checking people in. So maybe instead of waiting an hour with grandpa to get the rental, everyone is waiting an hour to just check in because now the counter is understaffed.
Plus, I’m sure Disney has waivers of liability in place, but still probably has to deal frequently with ornery guests that refuse to believe it (“I certainly didn’t damage the ECV, Disney must have done something to it after I dropped it off!”).
It makes total sense to me that they would limit accepting drop off without the customer being present to just one company that is smoother and easier to work with rather than having innumerable headaches from services that may cause them regular problems.