Why do people like Matrosk (mkv, etc.) so much?

Question

Video

I read specifications and I can't understand people's attachment to mkv files. What's so special about this container compared to, say, mp4 ?
mp4 supports many tracks and subtitles, streams normally over the network and rewinds. Specifications are open. It is supported by almost all modern players (hardware and software). In addition, it, as for me, is simpler and less confusing.
Why upload it to mkv, download mkv, and then complain that the player is rotten and won't open?

Answer 1

On the Far East torrents, in particular Japan, China, nesting dolls are a vital necessity.

Answer 2

For anime, matryoshka became the de facto standard many years ago.

Answer 3

First, a breakdown into chapters. Secondly, any subtitles and fonts.