The answer to that is in the Zooko's Triangle link, give it a read.
But, in short: for a name to be useful in a global context, it has to be unambiguous or unique. If there isn't a centralized naming authority / registry, then that means that you can't be able to pick an arbitrary name. (If you could, you could just decide to use the same name as someone else, and now there's no way to figure out which one of you the name indicates.)
But, in short: for a name to be useful in a global context, it has to be unambiguous or unique. If there isn't a centralized naming authority / registry, then that means that you can't be able to pick an arbitrary name. (If you could, you could just decide to use the same name as someone else, and now there's no way to figure out which one of you the name indicates.)