They were gate keepers because there was an editorial standard to uphold. That's what gave them credibility.

If you run the magazine Food & Wine and you just publish random recipes that you found for free in church-ladies' xeroxed recipe pamphlet, you're going to lose your readership pretty fast.

Of course, some magazines applied more standards than others, and so that's when the reader learns to trust the recipe in Food & Wine (or whatever, I'm not recommending them) over Reader's Digest.