It's no secret that the passing numbers in the NFL keep climbing. Analysts have been calling the NFL a passing league for the past few years, but the truth is it has been so for two generations, and there's no end in sight for passing's ascendancy.
He does a good job looking strictly at the numbers. But one area I think worth discussing is the widened talent pool of potential NFL QBs. For much of NFL and college history, only white guys were QBs. Given that non-white guys make up a significant (if not the majority) % of the other positions on the field, it would make sense that when you start letting non-white guys play the position, you get an influx of talent. Combined with that new talent, you push out some of the less talented white guys who may have been holding onto positions simply because of a lack of resources. So now the NFL is choosing from a wider, more talented pool of players.
This also works for the type of QBs the NFL is choosing from. Because of shorter QBs like Drew Brees and Russell Wilson, you would think teams are more willing to acquire and play guys who don't fit the traditional prototype of what an NFL QB has to be. Similar to size you also get QBs more willing to move out of the pocket, which is where I'm almost certain the data would say provides good passing numbers when they throw, not to mention the fact that this just wasn't a thing until fairly recently in the sport.
And finally I think part of the better passing is simply the across the board better athletes over time. When you look at track you see the same thing as passing, consistent improvement. This encompasses a lot of things; better training (chemically-induced included), longer training periods, more specialized training from a young age, probably more sophisticated offenses in high school, etc.. By the time guys are getting to college they're good, strong athletes with good skills. They leave as really good, really strong athletes with very good skills. And they spend a few years in the NFL reaching elite levels.
Combine better athleticism with the fact that a current rookie in the NFL like Dak Prescott has probably seen more coverages and thrown more passes than a rookie in the NFL 15-20 years ago. Combine that with the increase in technology that allows coaches to better see what happens on the field and more/better analytical approaches to the game (though the NFL seems to lag behind other major sports here) and I think this goes a long way to explain why passing numbers are exploding.