Whenever I see someone with a BPPV diagnosis, I rarely see it as the only reason (if a reason at all) for the dizziness. When BPPV is clear and the only issue, it is pretty easy to treat nearly every time (1-2 sessions with near if not full resolution)
For example, I had a recent home care patient (female, late 70s) with lateral/horizontal BPPV (cupulolithiasis) but neck pain with relief of dizziness with cervical distraction. However, also had a history of eustachian tube dysfunction, cardiac problems, and deconditioning which could indicate potential orthostatic hypotension, chronic GI problems including frequent diarrhea (every 1-3 hours), and a few other things. However, there was also stress of a daughter with frontotemporal dementia, hoarding behaviors, limited social interactions, aberrant sensitivity to pressure, difficulty sleeping, fear of falling, etc. So I addressed what I could related to the structure (conversion of the crystal to a more advantageous spot and getting it out of the canal). However, we then addressed the fears and pain through recognition of the behaviors that were exacerbating her symptoms such as helping her find better balance and increasing her tolerance to movement (some simple exercise), helping her find good rest (positioning for comfort), calming her system (reducing fear response with movement through visualization and graded motor imagery), and giving her external cues based on the calming imagery (moving like a wave versus telling her how she must move).
Other vestibular diagnoses are limited in their use though I think they may be more common such as Persistent Postural Perceptual Disorder (PPPD) and Mal de Debarquement. Unfortunately, well-meaning PTs do not want to break from the BPPV model because they can explain it more easily. The problem is that a functional neurological condition such as PPPD does respond to an Epley maneuver, but it likely only harms the patient as it gives a false hope with the mechanistic/structural explanation. In that sense, I would say it may not truly be a placebo but rather digging the patient down into their condition…in other words iatrogenic harm. The problem that I have found is that no matter how much you try to show a patient or even tell them that their PT was not really helpful before, the amount of time, effort, and money they put into that person does not allow for them to change their mind. A way I have reframed the benefit of the movement is that it is an exposure to a movement that is novel and it gives the opportunity for their system to build confidence, which can be done with plenty of other movements too…and then we work towards breaking free from that model of BPPV and only return to it if the signs and symptoms are clear.
I could go on about this because I normally do, but I will summarize: Dizziness can always be a functional neurological symptom, and I believe the science supports that an element of it is nearly every time as distress is common.