FYI I only started watching American football after high school, previously I was only exposed to soccer.
I think the rules of American football is more modern. Its designed such that
* it's easier to score or come from behind in the last 5 minutes, thus making the spectator sport more exciting. More "dramatic" so to speak.
* when a coach is taking a gamble, its much easier to see to the outsiders, so its beginner friendly.
* More violent, I like watching guys fly.
* Easier for small time teams to win, thanks to a good salary cap system, as opposite to the no-cap system in baseball or soccer. This last item is what I use to prove why NFL is "better" than international soccer leagues. If you don't like it, suck it.