Why can’t you hold The Breather by your teeth? How does that affect the training?

Why can’t you hold The Breather by your teeth? How does that affect the training?

The mouthpiece is ergonomically designed to support people with poor lip strength and to prevent air leakage due to tighter lip seals.
It also stimulates the muscle network around the lips.
Holding the mouthpiece by the teeth puts undue pressure on the jaw and makes it harder to achieve a lip seal around the mouthpiece.