If stb do anything when...
A stb is designed to minimize lateral flex between the strut towers and help maintain steering geometry. Making it adjustable would have you moving the upper a-arms, upper ball joint, steering knuckle,etc. and stressing the front clip by trying to move the sides closer together or farther apart (this alone would make trying to adjust the space between the strut towers very difficult).
Having a rigid chassis is essential for good handling and the stb helps tie the two sides of the front subframe together more rigidly which will, at least to a small degree, make the car handle better.


