Why are you assuming there are always other jobs available? In the case when there is, I can see your point. But when there are not it's no longer a choice. Sometimes it's better to just things off of the table to make the whole system better. And yeah it does suck for people in unique circumstances. It's really a balancing act that requires nuance and compromise.
If there aren't other jobs available, you haven't made the whole system better.
I'm not convinced that a higher level of "no job at all" is a better overall fit for society than "some people drive Uber" given that Uber isn't a particularly exploitive thing in terms of destroying the body or inflexible hours or other problems of the past.
It seems like we're trading off a useful form of semi-employment for a greater need for direct redistribution, and I'd rather my redistribution be partially-Uber-shaped and provide at least some features.
A world where Uber exists needs a less-high absolute redistributed benefits floor, and results in some more work getting done to people's benefit.
The problem is, we just are really bad at providing that base benefits floor, and we're trying to make Uber magically fix that for us.
And if there is an actual reason, why take that option away from someone who is choosing it on purpose?