Well, there was nothing stopping anything from doing it before, they just didn't know there was a desire for broadcast, or for the broadcaster to be uninterested in the connection of the listener.
A lot of the protocol is about making sure that things are authenticated and private. You don't want a second set of headphones connecting without your knowledge usually.
This also lets you broadcast audio encrypted, without drowning out other radios, and keeps the listener from being able to do normal pairing tasks like "download contacts".

It's obvious now, but that's only after years of everyone walking around with small radio linked ear pieces.

Batteries weren't strong enough for wireless headsets when Bluetooth was first released