Pretty sure Los Angeles had bad traffic way before Uber and Lyft arrived.
I distinctly remember staring out of the Hilton at Universal City in 2006, on my first visit to California, with a group of Canadians marveling that there could be a traffic jam at 10PM at night.
I don't think they're trying to argue that Uber and Lyft created LA traffic but I would agree that their arrival put more cars on the roads. There's a huge market of people who are willing to pay a little extra to avoid the hassle of LA public transportation and considering that, in general, people Uber to busy places (LAX, downtown, etc.), it's bringing more cars onto the already clogged roads that wouldn't be there otherwise.
I got stuck in a traffic jam on the 405 near LAX at around 1:00 AM on my second-to-last day in LA last month. I'd stayed late at work to sober up after my farewell happy hour. I don't know if it was an accident or construction or what that caused it, since I didn't see anything.
Also of note... don't most people use Uber Pool to save a few $?
Just a guess but if the route planning models are good then an uberpool with 2 passengers + driver qualifies for 3+ carpools and will be much faster than a car that doesn't qualify for carpool with a single passenger and driver.
I distinctly remember staring out of the Hilton at Universal City in 2006, on my first visit to California, with a group of Canadians marveling that there could be a traffic jam at 10PM at night.