Let's look at the trimmed portion of Maverick.
You talk of extending the turn Steve, but where is the room for the extension?
This portion of Maverick sits feet away from the nearby pathway and Thunder Canyon queue, and Intamin needed some way to reduce the g forces to an acceptable level in the S Bend (image was taken when the Barrel Roll was still in place).
In order to reduce gravitational forces, you either widen a turn, as you point out Steve, or you slow your speed.
With no room to widen Maverick's turn, Intamin went with the later option and slowed Maverick turn to reduce the g forces in the S Bend.
Changing our sights to iSpeed, the trimmed portion of iSpeed leads to a similarly tight S bend and turn.
In the same case as Maverick, Intamin needed to reduce gravitational forces during the s bend and turn, yet couldn't extend the turn due to the nearby monorail.
So, rather than extending the turn, Intamin installed trims.
Hmmm, seems like a pattern, doesn't it?
In order to reduce gravitational forces, a coaster will either be designed with wider elements or be installed with brakes; both offer the same solution of lowering gravitational forces during an element.
When there is no room to widen an element, trims are installed.