You would often not have wifi available, and you wouldn't want to have to type in wifi passwords to your camera all the time. But your phone will almost always be nearby and persistent bluetooth is easy.

Wifi between your camera and the phone. Or your camera and a laptop in your bag or whatever...

Problem is they have to disconnect from the current wifi ap to connect to the cameras ap which is inconvenient and means there can’t be a constant connection.

Wifi NAN could be used to solve this problem but I’ve not seen anything using it. Apple only just added support last year though.