If Uber unilaterally increased minimum salary, then those competitors would have to do the same, otherwise they would lose all their drivers to Uber. So, if Uber really cared about drivers they would just do it. Instead they are making PR stunt by "demanding" government regulation.

It's not actually a race to the bottom because it's still a competitive market. Even unskilled people have a choice between being Uber drivers or janitors or stock clerks or fast food workers, or anything else that someone will pay them to do. If Uber pays less than Walmart then people can quit Uber and go work for Walmart. That creates a floor for the pay of Uber drivers independent of anything the government does.

And if the government is going to do something, it's much better to raise that floor, which minimum wages can actually do the opposite of because people have non-monetary job preferences. If a $21/hour minimum wage appears then you have to pay Uber drivers $21/hour, but suppose they have $15/hour in expenses (fuel, wear and tear), so that's really only $6/hour. Meanwhile a work from home job might have paid $10/hour -- a real $10/hour -- but now that's well below $21, so is no longer available. So now you're paying $15/hour to make $21 instead of paying $0 to make $10, which means you make less, and Uber gets to pay $21 when they would have otherwise needed to pay $25 to actually be competitive. And the same thing (to various degrees) with ordinary commute-to-work jobs vs. stay at home jobs, or jobs with longer vs. shorter commutes or in higher cost of living parts of the city or that require some training or other expense that ultimately has to be paid for out of wages, or the job is just downright less of a grind and people are willing to accept less money in exchange for easier work. By removing options people used to have, you only make them more desperate for the remaining ones and require them to accept worse options even if they're better on paper.