They don't work for DoorDash however, they're contractors who are agreeing to terms with DoorDash.
Even in the US where tips go against wages it's not so bad, generally the first tip or two will cover the difference and workers are probably doing way better than that. Doordash on the other hand applied the same thing to /every/ order.
DoorDash can claim they aren't paying for the time, but for the service. And how long that service takes is the responsibility of the contractor.
Is it dirty? Very. Does that make it untrue? No.
So the first step in any of these cases is to get these gig economy apps to admit that they're just trying to circumvent wage law by classifying employees as contracted services.