Quicktime allows Renoise to load MP3, AAC and OGG samples. I don’t personally know the full reasons behind the Renoise team’s decision to use it, but I assume that some thought went into it, and it was eventually decided that Quicktime would be a good choice when considering both Windows and Mac users. It’s just one of those packages that pretty much everyone has installed in some form or another.
https://forum.renoise.com/t/importing-mp3-audio-install-quicktime/27287