Then you'd be encouraging migration from every other industry into Uber/Lyft because, as you say, no other job offers the same flexibility. So why would I work anywhere else if my minimum is the same? Mostly benefits & inertia of life inhibiting trying new things will prevent some of it but there will still be meaningful migration. The de facto wage would probably raise a bit as competition for workers ripples & Uber/Lyft would start implementing caps on how many drivers there can be (because a lot more will still value the flexibility highly) to better control their prices since the demand pricing has a legal floor above the market rate.

This is all obviously assuming there's about a stable mix of minimum wage jobs available in the market to people who need them. Remember that this job needs a new car every few years so there's a bit of capital investment required to maintain this job. There are financing options available but now suddenly this minimum wage work is further costing you even more to pay the financing. Then you're left trying to address that.

Every legal change to the market can have unintended consequences and infinite imagined ones in advance. Some times it's better to just stick to simple tweaks/changes that have a pretty well trodden path of study by economists. It is also important for cities to explore different things too though so that we can collect the data but which city really wants to do that with its citizens, especially how hard it is to pass helpful reforms for which the market response is well-studied and the law easy to explain to people.