Why? Who gives a shit. I played football for 17 years. I have a really good understanding of the game. I know a lot about OL play especially. I've seen kids who have never laced up a pair of cleats who know infinitely more about the X's and O's of the game because they play Madden constantly. My point being that there's all kinds of different ways to understand and be knowledgeable about the game and none of that matters in terms of fandom.
I like new fans. Holy shit I would be in heaven if I was on a 12 hour flight next to an unknowledgeable football fan who asked me to teach them the game. That would be the quickest 12 hour flight in history for me, probably the opposite for them.