I think what was needed for the drastic change was, first, the threat of competition, and second, applicability of at least some portion of current skills and assets.

Could oil companies or coal power plant operators work outside fossil fuels? I guess oil companies could still do solar or wind projects because they have project management, engineering and offshore knowhow etc, often in challenging countries. They could also develop alternative fuel refining and distribution. They also have good investor relations. I think BP at least attempted something like this.

Coal plant operators could operate many other kind of power plants too.