simple, basic economic. Demand v supply. Supply will increase until demand diminishes. The cities see them as cash cows so they will jump into the mix until they cost more than they bring in.
Instead of asking the question "why are there more bowls", you should be asking "what are all these bowls doing that makes everyone want one". Go look up the tax revenue for various cities that have a bowl. Keep in mind these are held during normally dead periods in the tourism business. Hotels fill, people eat and drink, cities rake in taxes. Economics, my boy. Maybe a little Andy Spiva would do you good.