I think that people like the idea of buying unknown coins the larger exchanges haven't listed yet. In most cases when these coins end up being listed, they pump hard and that may very well be what people are after. Greed it is.
People will only realize that it's foolish to use these exchanges when they go down with all of their funds. Unfortunately, losing funds is the only way people come to sense....
Again, there are already exchanges that dominate the provision of these widely "unknown" trading pairs as well.
Even though theoretically you could still make a new exchange, list new coins that no one else has listed, and in turn get some trading volume, it's going to cost a lot of money and effort. Who is going to come to your exchange to list their coins when there are tons of better alternatives?
I think that it's possible with lots of funding, a good team, actual innovation and entering in the market in an opportune time as I mentioned. But if these factors aren't satisfied then I don't think that it's feasible.