One of the problems to consider is GitHub was considered the obvious choice for a while now. Therefore a huge developer base and ecosystem was built around it. Moving elsewhere would sort of alienate us from that ecosystem. Fragmenting the ecosystem again.
Hopefully what will happen in a foreseeable future is some general (on an ecosystem level) recognition of the problems involved will emerge and some settling solution will be the outcome. As the truth is we didn't move to CodePlex but have selected and moved to GitHub in the past. And that in my opinion does play an important role.