So will most marketplaces. Ex. if you decline too many guests on Airbnb, Airbnb will also kick you off.
Airbnb is a special case because there customers are picking a specific location so refusing cancels the transaction.
Uber wants to have the anonymity of Mechanical Turk with the Airbnb lock in.
I honestly fail to see why what Uber wants is in any way relevant here.
Seriously? What Uber wants constitutes exactly half of the argument.
This is not so dissimilar from the McDonalds manager that gives his employees an unpaid two-hour break in the middle of their shift, but fires them if they leave the franchise during it.
If you want people to be available for a period of time, pay them by the hour.
If you want to only pay people when they are working for you, don't call them a contractor, but prevent them from moonlighting.
How does Uber forbid moonlighting?
I know tons of drivers on both Lyft and Uber.
Uber is not paying people to be available and does not require you to work a certain schedule. They're paying you only for rides you pick up.
There are arguments for classifying drivers as employees, but time isn't one of them.
There is only one reason for this policy - discouraging moonlighting.