The ONLY time I've ever seen it used successfully was to make changes to the layout of ads, making them look like more organic content or likely to be accidentally clicked. You can see this at work if you've ever clicked on an ad by mistake, or maybe you were trying to close the ad and noticed someone has "optimized" the close button placement using one of these A/B tools.
There it is, that's the market for these tools. That represents the vast majority of the these companies use-cases, revenue and usage. Anyone else who implies an innocent intent is either ignorant or inexperienced.
Experimentation works best when a) it's easy to try different parameters for a thing, and b) there is a lot of money involved.
Your comment is weird to me because you seem to be implying that experimentation is a cult because there are no things worth optimizing, and/or optimizing things has a negative societal effect. Those things are obviously true some of the time, but it's not very interesting.