Apple has had to learn this lesson a few times too. It always sounds cool to an engineer to propose "let's blend search results from the local hard disk with those from the Internet" but almost all users make a clear distinction between "stuff I have locally" vs. "stuff out there on the Internet" and they don't want them mixed.

Largely because they know stuff on the Internet is potentially dangerous and full of ads and their own stuff is not, so they want the two sources (and the search mechanisms thereof) kept distinct.