Google Code was such an improvement over SourceForge. I think the real problem of Google Code was that it took them too long to support git. When GitHub started Google Code was still SVN only and later they only added Mercurial support. This made people look at GitHub and GitHub could shine with some new ideas, like making code contributions extremely easy and placing the code first. Which of course further increased the popularity of git and so on. By the time Google Code added git support many major projects had moved and GitHub was simply the place to be.