I take it you don't have real world experience with product management?

Adding options isn't free. If you drop a feature you can delete the code and stop testing it. It you make it an option instead, you need to maintain and test two features instead of one, even though one is only used by a tiny minority of users. If you have N binary options that creates a total of 2^N different configurations. If the features are perfectly orthogonal you only need to test N+1 things, but in reality, features may interact in unexpected ways, and you may have to test a significant subset of 2^N combinations to make sure you've covered all real-world scenarios.

And you will still get confused users. “Why does Bob get different results than me? Are you profiling me?” Alice complains, forgetting that she had turned a feature on/off in the options. etc.

That doesn't mean you should never add any options: many products require a certain amount of configurability to adapt to different user needs. But there is a cost to adding features, and a product manager should carefully consider the pros and cons. If “just make it an option” is your answer to everything you will end up with an unmaintainable product that is likely to confuse the majority of users.

I hear you, and yet DDG takes this to the extreme by maintaining completely separate frontends for those who don't want to run JS or want to sidestep the getting-started hand-holding (https://html.duckduckgo.com/html and https://start.duckduckgo.com/ respectively; while digging into that, I also learned they have https://lite.duckduckgo.com/lite too for whatever that does)

So a hypothetical expert.ddg.gg wouldn't be out of character for them

I am aware that there is a slight nuance here between what one may consider just theming of the frontend versus potentially changing how query syntax works, but I just wanted to point out that DDG has embraced UX-flags-via-domain-name which would be in-your-face different from some secret toggle on a settings page

Or add a button, etc.