You misunderstand my comment. Understandably so, I can see I wasn't as clear as I should have been. Let me clarify: Twitter has already spent a lot of money developing their own infrastructure. They now get to enjoy significantly cheaper ongoing infrastructure costs versus the cloud, as per the sibling comment. Moving to the cloud would be "throwing money down the drain" because they would have to invest significant resources into the migration and only have an increased monthly server bill as a result.