The same could be said of the taxi medallion system. Low-income drivers with illiquid value for their time, with most of the value going to medallion owners, car owners and dispatchers.
I feel like I'm of two minds about this, as all of the pieces from rags like the NYT use analyses that assign 100% of the depreciation of the car to driving, which is obviously absurd: your car loses something like half it's value the minute you drive it off the lot. For some reason, none of the analyses I've seen attempt to address this (in fairness, it's probably pretty difficult).
The upshot is the difference between unlocking wealth that was going to be unlocked anyway, and unlocking wealth that was going to be wasted. A person's car is a criminally underutilized asset (from both a personal finance and a societal perspective), and increasing its utilization so you get more value out of it during its trip from full value to $0 is a concrete gain for both society and the Uber driver (and along the way, passengers and Uber itself).
The dynamic you describe is certainly a factor too; It seems to me to be an open question how big a component of an Uber ride's value each of these is. At any rate, I don't think your confident assertion that being an Uber driver is simply giving up your liquid asset value is warranted.
So they may be "unlocking wealth" today but in the long run who really knows how much of that "wealth" they're really benefiting from if any at all.
Why don't they do that then?
example: uber is a marketplace for transferring illiquid wealth assets from drivers to uber itself, along with a fraction of the revenues from each ride. put differently, uber may be making its drivers poorer in an abstract way which they may not understand because they are being paid for the labor required to extract value from their vehicle.
another example: freelancing platforms. everyone knows that these platforms depress wages for the freelancers and are a race to the bottom. businesses can grow more because labor costs less on the platform than off of the platform, and they can expect the platform to handle the infrastructure of paying and managing the labor to an extent. but freelancers on the platform could almost certainly make more money if they weren't on the platform because then they wouldn't be competing with as many others for a given opportunity. sure, some people make it work. but on average, people earn far less and expectations are much higher.