In Stripe's case, the docs are all rendered server side and are viewable without Javascript.
I'm not sure if you can hook into the native CTRL + F search tool and see what a user typed (my gut says no way there's an API for that), so I guess Stripe just wanted to track as much information as possible on what people are searching for, even if it makes the user experience a lot worse.
The docs are indeed viewable without JS[0] (in a limited way) but the default experience relies on JS to render text.
We don't render all content on the page at once for performance reasons, which is (as a sibling speculated) the driving reason for overriding cmd+f/ctrl+f by default.
I hope to write an engineering blog post soon about how we build the Stripe api docs, with some focus on the performance and UX tradeoffs at play here.
I'm not sure if you can hook into the native CTRL + F search tool and see what a user typed (my gut says no way there's an API for that), so I guess Stripe just wanted to track as much information as possible on what people are searching for, even if it makes the user experience a lot worse.