There is a programmable search feature [0] that lets you limit search to a defined list of sites. Someone did a ShowHN a few months ago where they had built a programmable search with 200ish common sites that a stereotype HN reader might like (software documentation, wikipedia, reddit, some news and other media, etc), and it was actually pretty good.

I've said before, google is now basically what I'd call a "smart" portal site. For most stuff, you already know the handful of sites you might want to look at, and google just sort of brings you there from a relatively clean interface, as opposed to a traditional portal that would have lots of categorized nested links to traverse. In most cases you're not searching for a random site that you wouldn't know existed if it wasn't indexed, like in 1998. So the whitelist approach actually works pretty well.

[0] https://developers.google.com/custom-search/