Yeah, this is a good point. Imagine immediately playing a game of Starcraft with no knowledge of the units and how they interact with each other and not even any real good idea of what you're supposed to do with an RTS game in the first place. You'd spend 20 minutes floundering about and get murdered by an opponent that knows what they're doing. You have to learn what each unit does and how they work together and how to get resources etc etc somewhere. Usually it's in a campaign that drip feeds the tutorial at once.

A board game that's designed to be an isolated game session that plays in about an hour simply can't afford to drip feed rules to you over the session, because by the time it finished drip feeding you the rules, the game would have been finished already.