I'm looking at the running game as a whole, not just the starting RB.
2009 - 1492 rushing yards, 29th in league
2010 - 1616 rushing yards, 22nd in league
2014 - 1441 rushing yards, 27th in league
Trubisky had a decent running game in 2018 with 1938 yards rushing. Cutler only had that amount or more twice in his 8 year tenure with the Bears.
You are confusing total yards with an actual weapon on the field. Part of Fortes game was receiving yards out of the backfield.
Teams had to account for this and actually put people in the box.
the Bears 2018 rushing game was helped significantly by Trubisky running the ball. The load back, Howard, was somewhat pedestrian last year.
Montgomery production was extremely pedestrian.
The whole point of the running game is for defenses to have to account for it. No team feared the Bears backfield this year. Hence why they saw a fuck ton of base and nickel/dime D. That hurt Trubisky.
Teams had to account for Matt Forte's production on the ground. His yards per carry was pretty damn good and his short pass production was good.
So when you just point out total yards you are not getting a realistic picture of the force that Matt Forte was and the how the defense had to account for him vs what defenses did vs the Bears this last year.