Lyft/Uber can upgrade them to employees but the arithmetic of bottom-up economics means Uber has to raise prices to cover full employment benefits. The raised fares conflict with what passengers are willing to pay. E.g. even though yellow medallion taxis often cost more than Uber (especially for suburb trips) -- those yellow cab drivers were not employees with benefits like unpaid leave and healthcare.
I believe what this really comes down to is that society is not willing to pay the higher prices for drivers to be treated as employees. Same situation as not willing to paying higher prices at hair salons so hair stylists are full employees (instead of being contractors) with healthcare. It does seem like constantly blaming Uber for mis-categorizing employees conveniently shifts the blame from the society/customers. The extra money to pay the drivers comes from the passengers.
Let's look at comparison cases: The city of Austin TX temporarily banned Uber from operating there. A non-profit rideshare (RideAustin[1]) was formed. Even though they don't have to implement the same business practices as Uber/Lyft, it's interesting that the RideAustin drivers are also independent contractors and not employees with full benefits. Also as far as I can tell, there is no worker co-op owned by the drivers anywhere in the world that treats members/drivers as employees with benefits. Why is that?
Serious question about the framing of ethics: if (some) drivers see an arbitrage opportunity because potential passengers think Uber-with-employee-drivers "charges too much" so drivers willingly choose a rideshare co-op that treat them as contractors to undercut Uber, are the co-op drivers being unethical towards the Uber-drivers-as-employees?
Yes, a judge can force Uber to convert everyone to employees but that same judge can't force potential customers to pay higher prices. The alternative entities of RideAustin and driver co-ops shows there's a limit to prices that ride shares can charge.