You're not going to learn a full complex ruleset in one sitting.Having a one page quick start of the game structure, allows you to get a feel for it before coming back for a deep dive.
Your brain has a foundation to build on when you read the ful complex rules - it wont feel like your brain is maxing out at 100%.
So the nuances can really matter. Even if you get the rules right, you don’t realise the importances of something until you play once or twice.