Because people like money. This TLD business literally invented a new economic activity, and one with great margins. It doesn't really hurt anyone, has little to no cost, and makes a pretty penny. People With Money love stuff like this; if tomorrow they could invent a marketable TLD system for physical addresses, phone numbers or anything else, they'd jump at the chance.

This is just how the capitalist world works: stuff exists to make money, everything else is a bonus.