They have their scope. It's a video transcoder. Programs are better suited to doing their job well rather than stretching themselves thin with loads of features.
Then why can we apply video filters etc. if it is only for transcoding? That is a really basic thing. Like no audio or pass through.
You can also add subtitles. Why not audio?
I'm not a developer. Just explaining why projects keep within their scope and don't bloat their software with features, which in turn take more effort to maintain.