I work in ortho and there are a few things going on here.
Very often a broken brace means that we can't progress onto the next wire and so delays treatment, sometimes by several visits depending on the breakage.
The longer braces are on teeth the higher the risks are, especially around root reabsorption and decalcification, both of which are permanent.
Risks vs benefits have to be considered and if the patient is at high risk of permanent damage due to short roots/high sugar diet/poor oral hygiene etc. it's hard to justify keeping braces on when treatment isn't progressing.
All clinicians should be monitoring breakage rates and trying to help keep them to a minimum through education around diet and good brace care, and by making sure the patients teeth aren't biting off their own brackets.
It is our job to make patients aware of what's going on, and sometimes "We're finding it hard to move up the wires due to repeated breakages, I really need you to stop chewing gum if you want these off in the 18 month time-frame" can be reported as " I got shouted at/she said they're never coming off" etc
Some orthodontists have terrible chair-side manner and many have collosal egos. I've cringed hearing the way some speak to patients.
You also get patients who swear blind to you and their patents that they're doing everything, as instructed as you pull strings of chewing gum or jumper sleeve fluff from their wires, or look at their florescent blue (sweet induced) tongue or their bottle of licozade in their blazer pocket.
The most common reason brackets come off is diet-related but it can be chewing pens or sleeves, picking/pressing at them etc too. Anything that applies excessive pressure.
It can be tricky if a tooth is very out of line compared to the tooth next to it, you need to put pressure on it for it to move, but too much pressure might mean the bracket pops off, often during the appointment or very shortly after.
It can also be clinical factors like poor bonding technique or poor isolation (lots of saliva everywhere). Less regularly you can get faulty materials or equipment. Sometimes the patient has little grooves or pits or areas where the enamel is slightly abnormal and this reduces the bond strength too, likewise if there's been a filling placed where we want to bond.
But ultimately patients should always be treated with respect and clinicians should always be working towards the best patient outcomes.