We bump what we think the community might like and is aligned with the site guidelines. And only to the lower half of the front page, whence it soon falls away if we guessed wrong. The posts aren't necessarily what we ourselves like or think is good; mostly we don't have time to decide on that.
It makes me feel worse. But I'd like to hear why you say that HN somewhat is an echo chamber, and what you think would make it less of one, or where you might look for examples of non-echo-chambers on the internet. You're welcome to reply here, or email hn@ycombinator.com.
It's possible that you've observed something that's not on our radar, and such information is important for us to be aware of, even if we can't solve it by moderation.