But drivers can drive for multiple services at the same time, using whichever one is giving them a customer at any specific moment. I've talked to many Uber/Lyft drivers that use both apps at the same time.

On the consumer side, having the most cars available is not the only thing to consider. There's also price. For me, Uber is the first app I check (mostly out of habit), but if there's any sort of surge pricing going on, I'll check Lyft. If Lyft doesn't have a similar surge, I'll usually ride with them, even if it means a slightly longer wait.