Sprouter shutting down

They went from 'Twitter clone'[1], to adding formspring/Q&A features[2], to focusing on purely Q&A[3]. This looks like a good case to break down and see what went 'wrong'.

[1] http://www.readwriteweb.com/start/2010/02/entrepreneur-socia...

[2] http://www.readwriteweb.com/start/2010/08/sprouter-a-formspr...

[3] http://www.readwriteweb.com/start/2011/02/quora-for-startups...