There's no reason people can't make 30 seconds-long videos. Your crochet/knitting use-case sounds perfect! The problem is with how YouTube treats short videos as its own thing, expects them to be in vertical video format (because rotating your phone is asking too much) and completely messes up the UI (can't even seek properly). I think channels with short videos that teach a technique or a nugget of knowledge could be very popular and very effective (educationally speaking) if it weren't for the capitalist enshittification.