“Video player” developers don’t do any of the actual hard work, they just use ffmpeg, so it doesn’t matter how virtuous they personally are.

Crystal Player did not use ffmpeg. It came with a few codecs bundled, but you'd typically install a codec pack like K-Lite. Anyway building a fast and functional UI is actual hard work, don't know why you'd think otherwise.

K-Lite is mainly LAVFilter which is ffmpeg.