If that's all that is required to be an effective driver, why should cab drivers be overpaid?
This is why we have labour laws, to shift the balance, to make work suck a little bit less for everyone.
(In principle. In practice in the taxi-cab case, I can't say that the various regulations and systems improve things for anyone, it's mostly captured by the rent-seekers anyway, so everyone gets screwed)
Meanwhile, in the real world, people take jobs for all sorts of reasons, and often do not have the luxury of choosing freely. The whole reason we have labour laws in the first place is because the free market has shown, again and again and again, to be completely inept at guaranteeing fair tratment of workers.
I know that with a purely US perspective it's hard to see the benefits of labour protections, since here jobs are either unionized into stupidity, or completely at-will. There's no middle ground, and then it's fair to come to the conclusion that it's all crap. However, there are plenty of countries outside the US where job markets have a healthier balance between protections for workers and company interests.
Also, if the bar to entry into the profession is simply to have a car and a smartphone, it will quickly become a race to the bottom in terms of wages.
All of this is good for the consumers, they get a lot of power over the drivers, they can threaten to give them a bad rating and so on, but there should probably be a balance.
Then again, it's not like the existing taxi cab unions and medallion systems and regulations are a guarantee of a good environment.
And on the third side, this profession is going to be eradicated by self-driving cars within fifteen years, so who cares?