"On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity."
"Please don't complain that a submission is inappropriate. If a story is spam or off-topic, flag it. Don't feed egregious comments by replying; flag them instead. If you flag something, please don't also comment that you did."
"If they'd cover it on TV news, it's probably off-topic."
I find it useful to look at the submissions by the site's creator[1], before he passed over the site's management to others, back in 2014. As you'll see, it actually has very little engineering content, and on the contrary, has many articles from mainstream sources.
I'm sure HN has ebbs and flows on the ratio of engineering articles, but it was never supposed to be dedicated to those; maybe you just joined at a moment when the ratio was bigger.