Earlier quoted context omitted.
Because operating costs increased substantially because of the requirement to provide benefits to workers.
Why would increased operating costs mean they can't offer flexible hours to drivers? Setting and maintaining a new schedule would ADD to operating costs (gotta pay someone to administer the calendar), so there has to be some other reason. Is there some magical cost per-driver that nobody (even the Uber CEO) seems to be able to articulate? Stuff like withholding for W2s seems to scale really well. The only cost I can…
In other words, the same reason why restaurants don't allow a waiter to show up to work for 2 hours at 4AM.