Similar to what linuxftw notes, when Docker hit the scene it was basically competing with the likes of Heroku where you have a few common runtime containers on

Similar to what linuxftw notes, when Docker hit the scene it was basically competing with the likes of Heroku where you have a few common runtime containers on a shared runtime system. When trying to implement one of those you want to maximize some sorts of shared common components and page/file sharing to create some efficiencies in memory sharing/oversubscription.