So I was curious about how Pro Football Focus is able to grade all of these players, playing all of these games.

An analyst is either sitting at the game or watching the game online/ tv. They would have to track the performance of more than 44+ a game, determining what the player is supposed to do in a given situation. For example, the analyst has to know what each players responsibility for each formation. 

So lets look at just the top 25 games. 25 games x (minimum 44 players). That's 1,100 players that an analyst needs to grade. The amount of time needed to watch film for one analyst would be insane!

But lets say that they have a "team" of analyst watching one game that would help speed-up the process. We'll give them 3 people per game. That suggests that 3 people would again need to watch film together and come to a consensus. A little better, but still time-consuming. 

Lastly, the qualifications to work for PFF. Here is the link to their job list

• In this role, you will collect player and play-level data, which will be delivered to our vast array of team and media clients and drive our consumer products.
• Successfully complete an unpaid six-week online training program where we will teach you the skills required to be a data collector with PFF.

You can "love" football all you want, but what really matters is if you can understand the responsibilities of each player for a given play. I know there are basic position concepts, but not everything is standard. 

In conclusion, I don't see how these folks can reasonably grade a player without a detailed understanding of responsibilities. That is why the grades our coaches give are vastly different than PFF.