This doesnt sound accurate. I have trekked the Himalayas for over a decade - the risks of AMS are very real. Two people I have trekked with have died due to AMS on separate himalayan treks - both had trekked multiple times before, and were well aware of the risks. Both the fatalities were around 12000-14000 feet - much below the Everest Base Camp trek. When AMS hits, you need to descend - as fast as possible, with whatever means you have at your disposal. Otherwise you have unknowingly entered a Russian Roulette.

And Diamox is used as a preventative course for AMS - alongside excessive water intake - this is standard guidelines in all high altitude himalayan treks.

I got Acute Mountain Sickness at just 11k feet. Headache, nausea, dizziness, fatigue. I passed out until hitting the ground woke me up. I was very disoriented and vulnerable. If someone had told me that I had to get to a hospital or I'd die they could have led me like a tame goat. And they could be right. If you have high-altitude cerebral or pulmonary edema it is life threatening.

A guide getting a kickback can make it a lot more likely just by cutting short the boring acclimatization time.

Why would it be fixed? Insurance companies aren’t willing to invest in oversight, and everyone else profit, there is no incentive for changing the system.

What is less discussed is what happened to people who were able to identify the scam and refused to let it happen.

It percolated up. It’s usually what happens with corruption. If lower levels are found out to have a lucrative scheme, the higher ups (auditors, police, legislators) make a big fuss about stumping it publicly, but behind the scenes go and ask for a cut.

On the whole, there is finite capacity of certain assets, like helicopters. If the emergency carrying capacity is X and true emergencies are .6 X then there is spoiled capacity of .4 X, in which fraudulent emergencies are placed, keeping everyone in the system whole so that when true emergencies approach .9 X there is no need for fraud. This follows the "optimal amount of fraud is non-zero" and eliminating this fraud might remove the margin needed for the system to exist at all.

  An anecdote tells of the British government's bounty on dead Indian cobras 
  giving locals the perverse incentive to start breeding the snakes, to be able 
  to kill more of them and collect more bounty

Start of AMS like symptoms can easily be mistaken for walking fatigue and dehydration. It is easier to identify if you are at rest, but during the trek that is seldom the case. So when you actually start realizing something is wrong, you already are at an elevated risk. The only thing that works in these cases is to descend and as fast as possible at that.

Considering the fact that AMS will absolutely and a 100% kill you if you play around with it, guides presenting trekkers with an option of helicopter rescue is not that bad, at least if you look at the worst that can happen.

The only ill effect I can find from overconsumption is a "tingly sensation on the tongue". Of course, that doesn't mean the 'poisoner' wasn't ignorant of this, and genuinely did it trying to make them sick. Or maybe they simply said, "If you feel your tongue tingling, YOU ARE DYING!!!".

Make coverage void in the Himalayas... problem solved