You need VideoToolbox for this particular tool because it calls the VideoToolbox library from within FFmpeg in order to encode the video.
“Why do I need x264 to encode H.264 in FFmpeg?” is essentially what you’re asking. FFmpeg needs VideoToolbox support to work with my tool.
If you’re asking why I chose to use VideoToolbox in the first place, it was because I want this to be a macOS-specific tool with very fast encoding speeds at decent fidelity per bit. Hardware accelerated video encoding is one way to make this happen.
The fact that iPhones are getting this before Android phones without Google Play Services tells you all you need to know about the nature of RCS. Android has lost all of its intrigue and fun in favor of becoming GoogleOS