One major factor relative to all of the above is the rise of modern city and the middle classes that thrived within. Mercantilism and guild systems offered livable wages and new leisure time to pursue a self-conscious education. Incredible move beyond manuscript texts and wood-cuts. We can see Caxton's intro as move into modern information technology, esp in printing's ability to reach enormous audience efficiently and economically. Ideas, concepts grow and need to be communicated.
Language becomes a point of class-identity and status.
Thus, the human proclivity to rise, to gain, works to establish an identifiable linguistic pattern, a standard that will remain as long as their power base remains. Cultural implications are large here. English becomes a part of a national identity and thus brings with it a group who will want to control regarding this source of pride. After all of England's historico-cultural trials the language comes through as a modern, accepted European language. This is an advantage we still have in the sciences today.