Not that long ago, you could very quickly build a decent SEO campaign around "X vs. Y" tutorials and HN - write 5,000 words on e.g. Angular vs. Ember, get some friends to upvote it, and if you made the front page you'd be on the first Google SERP for Angular and Ember the next day.
I personally know a couple of early-ish YC companies who took advantage of that to boost their content marketing ops, and it wouldn't surprise me to learn that they were part of the reason this policy exists.
Nope - we just figured out one day that tutorials aren't intellectually interesting, in one of those obvious-once-you-see-it moments.
Edit: here's an explanation about this that I send to people who email "why was my thing downranked" when $thing was a tutorial:
Tutorials are not a great fit for HN. HN readers are looking for stories of intellectual interest that go deeply into a topic. Tutorials are great for readers who need to do the specific task the tutorial is about, but that is a small percentage of the total audience. Also, they tend to be directed toward beginners, which is wonderful, but not what the HN audience is looking for. Such articles rarely do well as HN submissions. You'd be better off writing something of general interest for an audience of smart hackers.
I personally know a couple of early-ish YC companies who took advantage of that to boost their content marketing ops, and it wouldn't surprise me to learn that they were part of the reason this policy exists.