In the same comment you say that the government has to help guarantee that Walmart won't exploit you in this banana purchase transaction by outlawing price gouging and monopolization. If labor is the same type of transaction, it stands to reason that certain types of employment can be exploitative, despite the 'voluntary nature' of the transaction. Is your issue with the 'Uber exploits their contractors' framing simply based in the fact that Uber has not broken any labor laws?
Since you're having trouble following me I'll give a quick summary here. You initially said:
> if all these drivers are getting horribly exploited why are they doing it?
My point is simply that this is crap reasoning: people voluntarily participate in exploitative interactions all the time if they lack genuine alternatives.