Why did it seem to stop?

Because no one was buying it any more.

From a 2011 article: "But sales plummeted to the point that the latest installment in the series, Warriors of Rock, sold fewer than 100,000 copies during its debut month last September."

It's so sad. It is so much fun. My boys and I love to play it so much.

yep, both that and Rock Band basically saturated the market by releasing too many variations too quickly

between both of them releasing 2-3 new discs per year, plus 3-4 songs of DLC per week, they quickly ran out of quality new content, and people got tired of spending more and more