Back in the day of yellow page advertising one of the barriers to getting business was placing an expensive advertisement in the yellow pages (for certain types of businesses). I can personally attest to the advantage of doing that. That is I was able to build a business from nothing ZERO sales to over $2m/year using a yellow page ad as the only advertising expense (also used direct mail though). Many of my competitors never wanted to spend the money for a similar ad. (You had to pay for an entire year). It just seemed to expensive to them. It was. That was good though, not bad 'psychological barrier to entry'. Back in the day it was several thousand dollars per month without knowing (the first time) what kind of results you would get.
My point is having to pay that money (and the effort of designing an ad and paying for it) showed commitment to what you were doing (at that time). It's just another way to differentiate from the competition. We were entirely self funded also and took business away from large corporations that did the exact same thing as we did. In the end having to pay for that ad was a good thing, not a bad thing.
I don't know all of google's logic with why they decide who gets SEO juice or not but I wouldn't discount what I am talking about as one of the reasons that things work this way.