I thought it would be cool to have my own TLD, but apparently it's all managed by the ICANN, so you can't just name your website with any TLD you want. There are different prices. But at least you can customize your second level domain. Why aren't TLDs like this?
In short, because of how DNS servers work. Each TLD has to be resolvable in the root servers and as far as I know ICANN doesn't manage root DNS servers and ICANN would have to become a registrar and coordinate all those TLDs with all the root servers all over the world.