Regarding teaching games:
I think 30 minutes would be considered a long time because in a lot of gaming groups, it’s usually one guy or gal who’s teaching all the games and is in charge of the “rules”. With miniatures wargaming I think it’s different because people are expected to have their own rulebook and armies to go with it. But your average boardgame, often you might have friends over at the house and maybe they bring some games or you have some games to show them and one or the other is going to have to teach the rules to the rest. And in the casual space, 30 minutes is the length of an entire “filler” game, maybe even multiple games if you’re talking about some quick card game.
In a lot of friend settings also, people may want to play multiple games over the course of an evening rather than one big, long game. Also preparing ahead of time doesn’t always work because sometimes you’re playing the game that looks appealing to everyone, rather than a specific game you have in mind.