Itsa lot easier to promote that if it is thousands of servers doing something fairly mundane where, worst-case, it not working means a tiny tiny proportion of your customers have to restart their video stream. So what?
But for a small hetereogenous business where what's happening has a much higher cash density, the actual practicalities of randomly killing things in production and the risk that represents rather get in the way, even though in theory you should be able to kill anything in production with minimal impact, you are much less inclined to take that risk when the stakes are higher.
As soon as chaos monkey cause a service interrupt for, say, traders - it would get turned off and whoever had such a bright idea fired. But if it causes a service interruption for a tiny proportion of people watching streaming videos - no big deal.
Its proponents just ignore this practical reality and seem politically unaware.
The difference between theory and reality is precisely the reason Chaos Monkey and tools like it exist.
What you're essentially saying is that in theory, these systems have been designed to be resilient, but in reality, they may not be. If that's the case, then you'd better verify your resiliency, because being resilient in theory but not reality isn't going to help you when your service goes down.