because in the year 2023, modern browsers are still sadly complete garbage when it comes to auto-playing legitimate videos on legitimate websites
the advertising industry f**ked everyone over in this sense, because they jammed all these terrible auto-playing videos with sound down everyone's throats, and then browser companies tried to stop it but there were casualties along the way of what used to be good functionality
that said, we can probably optimize it a little better, but it's very sketchy and works totally differently across iOS, Android, desktop browsers, etc.