MusicBrainz doesn't seem to appear in many search results?

That box already uses MusicBrainz metadata (which is sometimes annoying, see this thread, but that’s a separate problem).

We didn’t pay a lot of attention to this historically because we used to want to avoid getting traffic from Google - in fact, we used to block indexing fully for many years. This was mostly due to a (hopefully baseless?) fear of an influx of new users overwhelming the site without taking the time to learn the guidelines and decreasing the quality of the data. That said, you’re right that if we’re going to be indexed we might as well do it as well as we can.