accuracy (not just completion percentage), who else was open, if the ball should've been caught, etc.

QBR is still a mathematical formula. It is more holistic than passer rating, but at the end of the day, it is math. An underthrown deep ball for example may still be caught and look great for QBR, but because the wide receiver was so open, PFF isn't going to give as much credit to the QB. In Jake's case, he made 8 big time throws. This means he is getting a lot of credit for a completion. All QBR sees is 8 completions, but PFF can judge the difficulty and the precise accuracy of the throws.

All completions are not made the same. All interceptions are not made the same. All touchdowns are not made the same. PFF is able to adjust ratings based off all those factors, while QBR just sees completion, interception, and TD.

How PFF grades:
https://www.cougarboard.com/board/message.html?id=33631222

What goes into QBR formula: