"Oh, I dunno, Calder. Maybe more like 80%, haha."
Okay, so I'm prone to a little hyperbole from time to time, but you raise a fascinating point. You're American. I'm British. There's a massive historical difference between the two. America is a comparitively young nation. So, in the mid 1800s, your country was still developing and expanding. Mine, on the other hand, was settled and, to a certain extent, "decided". Of course, there were social and technological changes and developments common to both, but, while your ancestors were hiding under floorboards, mine were digging coal and making pottery, as their ancestors had done and as future generations would continue to do. The nearest parallel I can come up with is that, perhaps, my ancestors had to hide (perhaps not under floorboards) from marauding Vikings, or, since I'm half Scottish, from "Butcher" Cumberland's redcoats.
In 1776, when your fledgling nation declared its independence - with the vast majority of its land-mass virtually unknown and unexplored - Britain already had over a thousand years of history which had directly shaped its, then, condition and societal framework. I believe the main difference is that your country's comparative "youth" gives it a vibrancy, almost an urgency, which we British have long forgotten, or with which we have lost touch. In addition, America is so vast, compared to a tiny island off the North-west coast of Europe. I sometimes wonder how people manage to live in a country which has more than one time-zone!
I tend to agree with you when you say " I think that there are stories for average people just living their lives, too," but such writing is rare and, I'd guess, limited to a blessed few extremely gifted writers. I'm thinking of Thornton Wilder's wonderful "Our Town", or, to bring it nearer to home, Alan Sillitoe's equally magnificent, but very different, "Saturday Night And Sunday Morning".
But, even in such "mirrors held up to reality" there is the drama of the unexpected - Emily's death in childbirth; Arthur's beating at the hands of his adulterous lover's husband. I suppose I'm saying that, even in the most realistic and "down to earth" writing, there is a need for such drama. It's what keeps the reader / audience engaged. I suppose, as writers, we are condemned to eschewing total realism in favour of that which will keep our readers' attention and leads them on to continuing to read.