It seems OpenAI has achieved more with this tech than anyone else, and this level of capability didn't exist before OpenAI, so there's a limit to what can have come from outside. It seems that Ilya Sutskever is perhaps the driving force behind this, and he was certainly there from the start and presumably had a huge part in pushing this line of Transformer research before they had enough success with it to attract a lot of outside talent (OpenAI is now ~400 employees).