Why did Stuart Zender leave the Band "Jamiroquai"?

I never knew until now that they were a group and not one dude. I always thought the guy who sang and was upside down in the one video WAS Jamiroquai. And I'll say this: When I first heard Maroon 5's "This Love" (if that's the name of it...you know..."this love has taken its toll on me, she's said goodbye too many times before...") ---I just KNEW it was Jamiroquai making a come-back, but now, I can see that the music wasn't really Jamiroqua, but that lead singer sure sounds like him to me. (Sorry, this isn't an answer--just yakkin..)