Why not open networks for arbitrary cargo delivery?

Amazon Prime Now just rolled out in my city and I made an order to see how it worked. But this post isn't about Amazon Prime Now, it's about networks. The person who delivered my groceries did so in what appeared to be their personal vehicle. This really got me thinking. There are many other types of delivery services where this is common. Uber, Lyft, et. al. are hot topics of conversation here, but there's many more. When you take your car to the shop the shop orders parts that are delivered from local warehouses in traditional consumer vehicles, pizza delivery drivers, numerable local couriers, etc.

Each of these delivery systems are siloed from one another. When the types of systems are similar enough you get silly/inefficient practices like Uber/Lyft drivers having two phones, one for each service. What we really need is a meta-service. One in which any arbitrary vehicle and any arbitrary driver can deliver any arbitrary cargo (human or otherwise). You have a single phone app which offers you fares to deliver an Uber customer, a pizza, or an auto part simultaneously. You pick the one you want.

This would completely change the world for these types of services. It would open up multiple types of cargo to drivers who could then always choose to deliver the product which pays them the best. Vendors could choose to pay at a rate commensurate with the urgency at which they need the cargo. You get much more efficient use of time because a single driver could pick up multiple packages from multiple vendor warehouses and deliver them to multiple destinations in a single trip. This would drive down the costs for everyone.

However, I don't foresee the likes of Uber giving up their firm grasp on the driver/vehicle. At least not yet. I suspect though, once actual human drivers are completely out of the picture these types of options may be more plausible. What are your thoughts?