You want to flip to something you know about where it is, you find it quickly.
I’m not talking about having to bring up the search function, type in some specific thing, then find it. You might not even know just what word is applicable.
Besides, so much with books is assumed you’re reading fiction stories. In non-fiction, there is much more variety and not just narrative text. In non-f, there are many more possibilities for visual cues where things should be.
Plus there is still more eye strain with digital pixels. I can attest to that.
I have a strong spacial component to my memory, so I have some books too in which I recall exactly which part of a chapter or page contains what I’m looking for, even when I don’t remember a particular word to do an electronic search. In general, though, I don’t think manual searching comes anywhere close to electronic searching.
As for eye strain with ebooks, e-ink devices (as opposed to ordinary CRTs) are easy on the eyes. Also being able to make the size of the print larger is a great advantage compared with ordinary books. The print in many conventional books is too small to be read comfortably by some persons (especially older persons). Cataracts have reduced my vision to no better than 20:30 in my best eye, but I can read ebooks with ease.