PFF focuses mostly on analytics. While valuable, analytics doesn't tell the whole story.
At the same time, much context is subjective. What elements together produce "context"? How much should each element be weighted? Are "gut feelings" (instinct) about players worth being part of player evaluation and selection?

In the end, the complexities of player, team, system, circumstance, injury, etc., are what makes selecting players so very challenging. And it is why good GMs can have a good run of success followed by mediocre (even poor) success. And then back again.