How often do medics tell you the cause of apnea, rather than just prescribe CPAP and forget

It's been about five years since I was diagnosed, still no word of what the actual cause is.
They gave me a CT scan recently to see what's going on. Five years seems a long time before investigating, although the pandemic happened and the NHS hasn't really recovered.

I ask the medics sometimes why it can't be done with ultrasound, which I would think would be great for looking at soft tissues in real time, and cheap and readily available but I haven't got much of an answer. Probably good reasons why not, if I thought of it I'm sure the pros have, but it's be nice to know.

I just want someone to say "bone there, tissue there, that thing there is why your throat is closing, and this is what can be done about it, and this is the professional who knows about it."
But it seems to be more piecemeal than that.

I had a GP called Kelly who was also an ENT specialist, seemed really on top of it, but pandemic came and he moved on.

Is there a list of doctors and dentists that are really into apnea and associated problems?

It certainly doesn't help when the pros disagree - like my dentist who said underbite was locking my jaw and wanted to file my teeth, and the other dentist and TMJ consultant who said that was nonsense.
Without my own physiology degree how do I make sense of that?