@revenant i'm *totally* guessing here but, i think it's because OPs tend to take an overwhelming percent of an episode's bitrate
you're supposed to use playlists or fancy embedded stuff in the mkvs to tell your player to sequence the OPs/EDs into the right places but most players probably don't support this
@notwa @revenant EEeh, I would be surprised to see openings/endings accounting for 20% of the episode's size (and 20% << overwhelming)
It still makes sense as an optimization, though, when you have a bunch of episodes packed in a single torrent, because the space savings are (n-1)*size, with n the number of episodes.