The Arcade days, Countrys ground breaking graphical capabilitys, and 2 big name develepors Rare/Retro working on the series, helped DK to form a sizable fanbase, not to mention that Nintendo actually treats the series like a important thing.
Yoshis games on the the other hand, never really generated much fuss(outside the original Yoshi's Island of course).....
And honestly, the Wario series isn't unpopular, I mean Ware is still popular and the Land series is fondly remembert by pretty much everyone who played them.
Nintendo just needs to give the series more love, advertise them, give them more exposure in Crossover games and treat it like it's important.
I'm certain that that would make series more popular, since you know, Wario the character is popular, his series just needs much better treatment.