Whether gig work is a side job or a main job is very context dependent. It depends on the availability of work in the region, the cost of living and a whole host of other factors, including the personal circumstances of the driver. One of the reasons ride-sharing companies ended up at this point with their workforce was because there are many drivers in California putting in excess of 40 hours a week on the road. Further, Uber in particular has regularly manipulated the percentage they take off the top as you have more rides or longer rides so drivers have seen less of a cut, making driving for them less competitive than it used to be to just join an actual taxi company, which seems crazy for those drivers (the majority) using their own vehicle. Uber and Lyft have pocketed vast sums of profits with only a small percentage going to drivers because of the independent contractor designation, very similar to the UFC. This has been exacerbated by the move away from rideshare only to different types of transportation and lately delivery of goods or food.
The business model will change, but you can argue it should've never existed in the way it does to begin with. A useful alternative structure would be for cities or whole states subsidize development of their own apps and move to a cooperative structure where the drivers received all of the revenue then devoted a small percentage collectively to (~5%) to licensing use of the app, which the cooperative or local government would own. In this model, workers would also be owners and could pay into healthcare, pension, etc. This model isn't unprecedented and had already been implemented in a number of places around the world. They're called platform cooperatives.