@volkris matroska was quite prevalent in the piracy scenes. i still see them from time to time with anime.

i think MP4 inertia is because big tech pushes it hard, so media players support it, which leads to being able to download and drop it on an iphone or some set top box share and it works.

matroska is like opus in that all the decent stuff does support it just fine. it's just not the lowest common denominator.