Hi there,
Yiannis makes some great points. Here are some more thoughts:
Are there other news outlets, forums, communities on Facebook, etc. in your space that you regularly communicate with? One reason the SEO community shares posts so often is that many people have been chatting to each other in a range of locations for years. They are not posting in a vacuum where they put up blog post links on their Facebook and Twitter pages and wait for shares - they have been contributing in various ways in a lot of places, Moz included, for so long that their peers share their work.
You will also find that there are a LOT of networks like email lists that deliberately share each other's content. They're all meant to be secret and they realistically are - no one who isn't on an individual mailing list knows about it - but if you watch social media closely enough within a niche like SEO, you can see the same people sharing each other's things. You can determine that they have either a mailing list or a private Facebook / Google group where members ask for shares. These deliberate shares always prompt "natural" shares if the content is good enough.
Getting friendly enough with people that you're included in these sorts of lists, or setting one up yourself, is a longer process that means getting involved with a lot of peers, even competitors, where they're hanging out online - talking to them on Twitter and Facebook.
At my former agency, a post on pagination - one of SEO's most "boring" subjects - got so much attention due to being well-written and shared by a few highly-followed people within SEO (including Rand from here at Moz) that it became the second-most visited page on our site behind the home page over an extended period. If we had simply been tweeting out URLs and titles, few would have read it. However, we shared it with friends and cited it where relevant and it was picked up in a big way.
I hope this helps!