I often ask Uber drivers the same and the response is generally:
* the pay is decent (ranging from a hair above minimum wage to a healthy and sustainable source of income)
* the benefits are non-existent (most don't seem bothered by this)
* the job security is guaranteed (a huge plus)
* the work schedule is at their discretion (another huge plus)
* the work environment is quite good (passengers are usually very friendly, you work from the comfort of your car, the on-boarding process is quick and painless)
All in all it's a net benefit for most people, in terms of quality of life and financial stability. What's not to love?
Note: this is all purely anecdotal and most drivers I have spoken to have been working for <1 year, in most cases <6 months.