I'm not making it up. Here's my source:
This is a compilation of the icv2.com retailer surveys of Top Five Roleplaying Games. They are generally compiled quarterly (with some exceptions). ICv2 notes that "the chart [are] based on interviews with retailers, distributors, and manufacturers." Thanks to jodyjohnson for sterling...
www.enworld.org
In Q1 2010, shortly after the release of 4E Essentials, Dungeons & Dragons lost the top spot for the first time ever, and kept falling. It eventually dropped all the way to #5, behind Pathfinder, Star Wars, Fate, and Numinera. D&D didn't get back to #1 until after the release of 5E.
Here are the relevant graphs:
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