In an interesting experiment, Uber is trying to reinvent the urban bus system. At first glance this sounds insane -- we already have a transit system and it is subsidized. That said, it has some pretty massive inefficiencies in it. Consider:
As a small example, I was riding the bus on Sunday and getting annoyed with how frequently it stopped. If you eliminated half the stops, I tweeted, the buses would go way faster and DC transit would be much better. Nobody disagreed with me but everyone pointed out the problem: better eliminate the other guy's stop, not mine. That's the logic of politics, so change doesn't happen. A private company wouldn't do that. They would ruthlessly alienate a noisy minority of customers in order to drastically improve service at zero financial cost.Not part of this argument is the odd cultural idea that private industry should favor efficiency above all else whereas the government should favor "accountability" or some such objective. That said, Houston (of all places) seems to have risen above these issues to create a much better bus system.
It also can't be a quirk of geography. Canada has the same basic geographical issues (possibly a tad worse but that can be debated) and manages to have excellent public transit. Just try taking public transit in Toronto to see the amazing difference. And these are systems that, as a user, I could see ways to improve.
The last piece here is that the biggest barrier to being 100% transit is to have reliable and frequent transit. I had this in graduate school and lived for five years without a car. During part of that time I was quite disabled due to an injury, and I found the frequent service made up for the longer walks between bus stops. Yes, you occasionally missed a bus. But when the next one was 10 minutes away it was a completely different type of disaster.