I think there are a lot of places around the world that have Uber but don't have Lyft. Uber has competition in some areas but it seems like there's a lot of places where it doesn't have much.
Lyft is only in the US, so yes, most of the world has Uber while only one country has Lyft.
Also Toronto now.
Sure, but wide coverage doesn't come for free. Uber has to set up regional offices, advertise to local drivers, etc. etc. in each city in which it operates. It's not difficult to make the business case that you should actually just focus on a small number of huge cities instead - your chance for profit is much higher.
I cannot really comment on the difficulty of making the business case for only huge cities. But I am not convinced that marketing to non-Huge cities isn't profitable.