RMS has been literally all about Free Software from day one. The term "open source" originated as a competing philosophy from Bruce Perens. It's like going to the CEO of Coca-cola and asking about Pepsi.
RMS was also a fringy fanatic from day one. It took a lot of willpower and vision to advocate for Free Software, a movement that that flew in the face of the overwhelming proprietary software industry that existed back in the '80s. A lesser person would have given up long ago.