Why "single" blind reviews?

A noticed that some journals adopt double-blind reviews, while some others "single" blind reviews: double-blind reviews imply that both the author and the reviewers are blind, while single-blind reviews imply that reviewers are blind and the author is not.

Despite the limits of "blindness" by itself (it is sometime possible to understand who is the author anyway), I find the double-blind review process more fair.

Why therefore do some journals opt for single-blind reviews (authors are visible to the reviewers)? What's your opinion about it?