All in all, text selection and search is still such a second class experience on iOS.
I have to admit I don't see where to put the "search inside the page" feature, definitely some ux trick to be found
So, back on-topic, it does kind of make sense in that you’re taking the current URL and sending it to the Springboard.
The best example is Photos, where the Share Sheet would have a LOT of unrelated junk — Duplicate, Hide, Slideshow… But as of one or two major versions ago, there’s now an ellipsis menu to keep those options instead. Notes got the same treatment.
In current Safari, the “aA” menu is an equivalent of that. In my opinion, “Find on page” is really the only option on that Share Sheet which doesn’t really belong. All the others make sense, as they’re an “Export” of the page in some way or another.