Many startups are 100% irrelevant there. Take huge poster children like Uber, for example: everyone has a car already, as it's basically mandatory. Or smaller startups, like Slice, for example. I live in NYC. I have lots of pizza options. I love pizza. In my hometown, there are two pizza places. You don't really need reviews, you order from one, and if you don't like it, well, you have the other one.
Now, that's not to say that there are zero startups that do; not that Facebook or Twitter are exactly "startups" today, but when they were, they still had a big impact. But a lot of startups are focused on "upper middle class people who live in population centers". That's a lot of people, but it also leaves a lot of people out.