Two reasons:1. No need to use anything other than Jack. Ardour now has got the option of not using Jack. Shouldn'thave been necessary.
2. It feels like a server configuration protocol will stabilize faster if clients also can function as serverssince more code is using it, not just qjackctl.
It works, but the more components you glue together, the higher the chance is for somethingto fail. For instance didn't the messages window in the windows version of qjackctl show anythingcoming from jackd until autumn 2015.