IFR flying can be quite dangerous, particularly when transitioning from the airport to the enroute structure and vice-versa. This "answer" should be taken as a discussion more than a definitive statement. See also this previous discussion: Why is the VFR traffic pattern area at some airports different from its IFR circling approach area?
Per the sectional (and AFD), Runway 20 is right traffic while Runway 2 is left traffic. Thus VFR pilots operating at VCB are restricted to remain west of the airport no matter which runway they are using. The AFD further states:
No turns to crosswind below 800' MSL, remain west of interstate
highway for Rwy 20, noise sensitive area west of arpt.
That noise-sensitive area appears to be the communities of Ridgeview and Browns Valley, and seems to present something of a contradiction. If there are noise-sensitive areas to the west of the airport, why should pilots be restricted to remain west? There must be a compelling reason.
As an educated guess only, that compelling reason may be Travis Air Force Base and its associated Alert Area 682. Note how close VCB is to the Travis Class D airspace: an east-of-the-airport pattern would put a VFR pilot uncomfortably close to if not solidly within the surface area, depending on the size of the pattern they flew. And note how the edge of A-682 nearly lies on top of Runway 2–20 at VCB: an east-of-the-airport pattern would be almost entirely within the alert area. Sure, it's not super likely that military trainers would be flying around right on top of another airport's traffic pattern... but if you have the chance to avoid the possiblity altogether, why not do it?
For IFR traffic, however, the calculus changes. An IFR aircraft operating in controlled airspace must be in contact with and under the control of an ATC facility—in this case Travis Approach, who is probably also talking to any military aircraft flying around in the alert area. So the question of violating the Class D is alleviated; I strongly suspect that Travis Approach has to coordinate with Travis Tower prior to clearing an aircraft for the VOR-A at VCB, and furthermore that when an aircraft has been cleared for the approach IFR traffic off of Travis is prevented from turning north- and west-bound.
Even more importantly, look at the sectional and the approach plate. Observe the rising terrain which comes to a peak only seven NM west of VCB at 2800' above field elevation; observe the obstruction only a couple of miles west of VCB at 700' above field elevation. A VFR pilot operating in the traffic pattern can easily see and avoid these obstacles. An IFR pilot executing a circling approach—with the possibility of going IMC and having to execute a missed approach—is in a much more dangerous situation.
Now for the legal aspect: in the Krug interpretation which you linked, regarding a pilot's desire to fly a circling approach contrary to the established pattern direction, the Office of the Chief Counsel said:
ATC may not issue clearance to conduct a right-hand turn at an airport without an operating control tower in Class G airspace. The Collins Interpretation notes that the circumstances under which a deviation from the left-hand turn requirement in § 91.126(b)(1) is "authorized or required" are very limited. Specifically, a deviation must be "authorized or required" by approach guidelines to a specific airport or by another FAA regulation.
(Note that ATC is not only prohibited from issuing circling instructions at Class G airports; they are prohibited from issuing circling instructions at all non-towered airports. This is not to say that pilots are prohibited from electing to circle, or not, on their own accord and to the runway of their choosing. Obviously in the case of a circling-only approach they must circle!)
To my reading of the letter, the approach plate restriction "Circling NA west of Rwy 2–20" is in fact a "requirement by approach guidelines" which supersedes not only the default left-pattern requirement for Runway 2 but also the specifically-published right-pattern requirement for Runway 20.