Despite my guessing analysis, I must say that I have also seen folks with moderately severe to severe and profound hearing loss who stick with their Oticon aids as well. So I wouldn’t say that my guessing analysis is universally common that it would almost always hold true in most cases.
I fully agree that there is also something else going on as well. I think one’s personal preference to the listening approach, or one’s expectation of what their hearing aids can do for them, would also play a big role in the suitability of a hearing aid. If you have moderately severe to severe hearing loss, but you really want to be able to hear more sounds, and you adopt a positive attitude and really give it a try with the Oticon hearing aid, maybe you’d have a better chance of making the Oticon aids work for you, as compared to someone who prefers to hear less sounds and just wants to understand speech better, tries the Oticon and the Phonak, and instantly like the Phonak because it meets their expectation better.
But there’s probably also some physiological hearing limitation as well. I remember @bluejay as an example. She tried the Oticon OPN and really wanted it to work for her, so she definitely gets points for having a positive attitude and really wanted to try, but in the end it just didn’t work out and she switched to the Phonak Audeo B Direct (IIRC), then Marvel and Paradise later, and it works out much better for her since. IIRC, she has moderately severe hearing loss, even at low frequencies.