When they talk about "shift work" they're referring to the way the taxi industry works. The reason the taxi industry works that way is because most drivers drive company cars which are owned & maintained by the company. Drivers that own their own cars can drive whenever they want to. There are no shifts.

I drove a taxicab for more than a year back in the 90's. That's the way it worked then. Most drivers were shift because they "rented" the car from the company and shared it with other workers. A few drivers were owner-operators who got to set their own hours. This is closer to the model that Uber & Lyft operate under today.

So when Lyft claims that they would be forced to enforce shift work on their owner-operators, this is a lie. There is already a model for this type of driving that predates Uber & Lyft and they're just choosing to ignore it now because it serves their current interests.