There is zero friction to install a new app and accept fares via that app, except perhaps how many ridesharing apps you can run at once on your device for accepting passengers.
The linked article says Lyft now have an average pickup time in SF of 2.5 minutes. Good luck bootstrapping to that kind of performance with a brand new ride share company starting from scratch.
Based on what I've seen, Hailo tried to buy their way into this market, albeit with the twist of using licensed cabs. Seems like they had little trouble signing up drivers (who were predisposed to distrust the UberTAXI) but my assumption is that they gave up in North America because they couldn't afford to keep giving away the free rides and discounts needed to build up a customer base.
Drivers using both Lyft and Uber is a perfect demonstration that they care most about the size and liquidity of the demand side of the market. They are using both in order to increase demand side liquidity from their perspective.