This was sort of a bug / Apple took it away…
(i’ve heard of stories of people getting it back by reinstalling, but ive done fresh installations recently and its no longer there)
Just use Compressor, or have DVDSP do the conversion for you.
Honestly i never ever touch the QuickTime Conversion export – always either export Quicktime and have a separate app do the compression, or export using Compressor (that way you can have watch folders and droplets already preset so you don’t have to do any extra preparation).