You might ask the same about any exploitive relation.

Why is there prostitution?

Why are slaves doing work for their masters?

Why are children going through our garbage in some distant country, if they hardly earn enough to eat?

i dont think the choice between driving Uber and working at Walmart is the same as being a slave or dying.

True, they are not the same. But they probably feel similarly coerced into accepting an unfair deal.

So yeah, the comparisons are hyperboles, but I totally feel why they're upset and hope collective bargaining helps better their situation.