FFMpeg is definitely fairly ubiquitous, but you are overstating its universality quite a bit. There are alternatives that utilize Windows/macOS's native media frameworks, proprietary software that utilizes bespoke frameworks, and libraries that function independently of ffmpeg that offer similar functionality.

That being said, if you put down a pie chart of media frameworks (especially for transcoding or muxing), ffmpeg would have a significant share of that pie.