Why are these TLDs so tightly bound to a specific organization? Why can't their registration be more open? Keeping them so locked down makes them useless. Or am I misunderstanding something?
Not quite, assuming we're not talking about .brand, they have to make them available for purchase by the general public. However, they do get to dictate prices.
https://newgtldprogram.icann.org/en/application-rounds/round...