The JWST’s field of regard excludes a significant portion of the celestial sphere in the anti-sun direction. See JWST field of regard (FOR) (source of the image below) Also see How much of the sky can the JWST see?
The spacecraft can’t pitch up to align the telescope boresight to within 45* of the anti-sun direction because the telescope would move out from behind the fixed sunshields.
Observatory within “Penumbra” of sunshield
Over a 6 month half-orbit of the sun, the entire sky is observable. But what happens if an interesting event occurs in the “blind spot”? Like Shoemaker-Levy or the arrival of Rama? A gravitational wave event?
If the observatory and sunshield were articulated to move 22.5* with respect to each other, the entire celestial hemisphere would be included in the field of regard.
It is not necessary to violate the single, rigid structure of the observatory to point it in a different direction. It is only necessary to ensure it is shaded in the new direction. This could be done by re-designing the sun shield to provide more coverage. The increased coverage need not be in all axes. Adding another 25* of rotation in the V2 axis would extend the field of regard to the entire celestial hemisphere. This would have no effect on reaction wheels, fuel consumption, failure risk or lifespan
Was this capability not seen as a design priority? I can’t imagine it would be a technical challenge.