To anyone else confused: ELI5 means "Explain (it) Like I'm Five (years old)." Now I'll try.
Caveats: I don't watch American football on TV, but I watched it some when I was a teenager. I mostly remember how to play, and while I don't think it'd be safe to do it at my age, I do like to play catch with an American football whenever I get the chance. I wouldn't mind watching a game now, but only live and very close to the field.
The thing is there's a lot of strategy, and each play is a meticulously, often spontaneously, planned action by the Offense (team with the ball) which the Defense does its best to disrupt.
That disruption is almost always at least partially successful, forcing improvisation on both sides. In particular the quarterback (guy who throws the ball) often has to rethink the plan in real time as people chase after him -- he really really doesn't want to be tackled, for his own protection as well as for the game -- and somehow make this work with people who are running around at some distance from him. When it works it can be awe-inspiring and utterly unexpected.
These things -- the strategy, the plan on the field, the disruption, the improvisation, the danger -- are all directly and intimately connected to the physical and mental abilities of the players, which are routinely pushed to their limits, sometimes to the point of causing permanent damage.
This is all the stuff of human drama, and as in most human dramas the decisive physical events don't take up that much of the time.
Another thing I'd add is that compared to a lot of other sports American Football offers an interesting combination of extreme chaos (the tackle, etc) and extreme precision (the long-distance pass to the wide receiver).
Soccer by contrast never has that much precision and is much more about mastering the ever-present chaos, most of it very slow paced; basketball can go long stretches without getting very chaotic at all despite things constantly happening. (I know some people will take umbrage here, but I'm ready to defend these points!)
I can't think of another sport that so closely tracks an idealized version of warfare and group combat. Though I'd love to see other examples.
All that said, familiarity has a lot to do with how much you can enjoy watching a lot of sports. If you grew up surrounded by the culture of Sport X there's probably stuff in it you will like to watch.
I like to watch squash, because I played it enough to understand what's going on. I have a friend who watches hours of snooker online. Even golf draws an audience. Even cricket!