Why I ignore them? They’re plain crap, as defined by my friend Ann Smarty’s infographic:
In sum, guest post solicitation spam is the new “can we trade links” email spam. People are scraping Google’s results for “guest post” + keyword, or “write for us” + keyword and auto-emailing the resulting list of sites.
It’s push button, it’s easy, you don’t have to take it personally when you’re rejected … and it’s utter crap.
Laziness doesn’t get you ranked, and shortcuts don’t get you ranked. This is not working smarter, it’s trying for shortcuts and wasting other people’s time very rudely.