They're buying them out for their mobile presence and the massive number of games they have.... Zynga doesn't make great games, they just are masters of psychology and monetization..
But hey, maybe Glu is a better buy than I thought.. I didn't get that impression when I last spoke with them, they didn't know many of the basic elements of social game design or programming. I was stunned this outfit was a public company with such limited knowledge...
But, time will tell, I'm glad to see the stock price start to rally back up... in my opinion though, I didn't think that purchase was good.