I guess, its the government, since people drive for both lyft and uber.
Uber is saying don't do that, instead proposing a new government policy (laws or regulation) of a minimum rate of $21/hour while providing a ride. Like minimum wage, this would be paid by the employer/client, but the government sets a price floor.
Note that how this compares to minimum wage for employees depends entirely on the occupancy rate for the vehicle: if you've only got a fare for half of the minutes in a hour, that's $10.50/hour which is under the 2019 California minimum wage of $12 or $11 for small employers.
Competition will keep the wages as low as possible so this change must be done at the systemic level so that Uber and all of its competitors have to make this change at the same time. The only forseeable way to do this is government policy.