True for you and many others but not a universal truth by a long shot. Blogging is far from a time consuming activity if you're both a reasonable writer and neck deep in the subject matter. Let's just take an example that sat on the front page of HN for most of today:
232 words. And as my own blog was on the front page a similar length of time today, I'm confident they got at least 2000 pageviews from that (I got 5000) and I know I've seen several posts of theirs do well here. Yet if you check their blog, they have several posts per month at most, none are very long or technical.
Other startups like SeatGeek and MailChimp nail the blogging in a similar way. There's no way they're not getting some serious exposure with them, yet it seems in most cases it's regular techs updating the blog and not some team of "noise" generating PR flacks.
Small Blogs are about personal brand, long tail keywords and SEO benefits. I sometimes talk about products, sometimes post big ideas, sometimes post about failure.
My guess as to your problems would be lack of customer contact the whole way through. Without knowing the problem domain, if you're concentrating on getting 'industry' PR like TechCrunch, you're probably concentrating on the wrong people. Assuming there is some type of vertical you're targeting (travel, photography, vehicles, whatever) thenyou should be making moves in that part.
My final thoughts on the matter : it would never even occur to me to try and get TechCrunch coverage or anything like that. I would just be trying how to work out how to find customers that pay. If you've spent a fortune on google ads, then you should at least know what works as a click through and what hooks to start working around. It's either bad conversions or a bad product. PR coverage won't fix either of those.