Seen from an ATCO's point of view, we are often told to "offer" shortcuts, in order to save fuel etc.... on the other hand, we are also adviced to be carefull to do so during the approach phase, since we're taking valuable time away from pilots.
So the best we can do is ask....
Then from the pilots point of view, some of us are a little "go" minded, feeling we're always ready for what ATC asks of us, we are always ready to help ATC.
So the best we can do, is learn to say "nope".....