People part with their money when you add significant value (solve a tough problem or create lots of delight). The value of Learnivore is that it collects programming screencasts into one place, which is
valuable but not
that valuable. It's not creating enough value that you could charge directly for it.
In order to make good money, you'd have to view the screencast aggregation as your marketing, not your product. You'd have to invent another product to go along with this.
Ads are a weak example of this. Ads would be about connecting programmers with businesses serving programmers, which you can see is a different product than screencasts.
Another product could be consulting. This site could generate leads for consulting gigs, which would give you more money in one hour than you can probably make in a month with ads.