I guess Rodgers knee injury is the main reason he doesn't step into throws like in past seasons.
That's an interesting observation. Rodgers has avoided throwing to the middle of the field more often this year (31.2%) compared to his last full season in 2016 (41.6%) for example.
I found the following pretty interesting which synchs with my eye test:
https://www.profootballfocus.com/news/pro-ranking-all-32-starting-nfl-quarterbacks-after-week-9
Rodgers: 4th. ranked from a clean pocket; 23rd. ranked passer rating under pressure @ 58.5.
I don't think what you quoted or the PFF analysis is about "stepping into the throw" per se. Clean pocket, squared up, no problem. That's a throw from a right leg plant, the good knee.
I see two possibilites, perhaps both a partial factor accounting for reduced middle throws:
1) I believe where he's been and remains limited is on the move throwing from non-standard body positions where there's a left leg plant and torque. In the past he's been a top passer out of the pocket where there are more pressure throws than called rollouts. Fewer throws to the middle may be a function of not having the confidence in accuracy to make the cross-body throw off the bad knee. We've seen a high number of throwaways under pressure, which could be a function of not having total confidence in accuracy on a tight throw on the move.
2) Graham may be factor. He draws a crowd in the middle of the field more than than past TEs, with fewer defenders on the perimenter. Further, the short money slants to Adams have been in short supply; that may be a function of another defensive body in the path because of Graham making those throws riskier.