I doubt that there are many Uber drivers that do it long term. Eventually at some point they have to realize that they're making peanuts (if not operating at a loss) after they factor in routine AND long-term maintenance costs of their vehicle. Or they simply get 'real' jobs and were using Uber between jobs or to supplement income temporarily.

The people I know that have personally done driving for these services has done it in addition to full-time work, largely hoping to earn decent extra money from tips.