I'm assuming this is just a matter of available space but it seems you could get 4 across all aligned but maybe there is another reason. The image is from McGuire AFB but I've seen this on other AFBs.
The main example in the question body is to confine the wing from the main taxiway, which runs across the bottom of the image.
It may not seem like it, but a 50 m (164 ft) wide plane like those tankers parked at a 45-degree angle saves ~15 m (approx. one-third of its wingspan).
The reference used by the USAF is AFMAN 32-1084 (PDF), from which:
188.8.131.52.1. Parking Dimensions. Table 2.9 presents the minimum geometric criteria for fixed-wing apron design. When designing new aprons for AMC bases hosting C- 5, C-17, KC-10, and KC-135 aircraft, provide 15.3 m (50 ft) of wingtip separation.
EXCEPTION: When you are rehabilitating an existing apron, provide the maximum wingtip separation the existing apron size allows (up to 15.3 m [50 ft] but not less than 7.7 m [25 ft]). This additional separation is both desirable and permitted.
By measuring on Google Earth, the angled spots are a perfect fit for the very large C-5 Galaxy, which has a wingspan of 67.89 m; halve that and add the 15.3 m clearance from the taxiway to check. A non-angled C-5 would violate that. (The measurement I made in the image below shows two half-span C-5s plus the clearance, with superimposed C-5s via pinterest.com.)
Being an AMC base, it's very likely those spots were made for the C-5 for whenever it visits.
For the other examples you've stated in a comment (Beale AFB, Tinker AFB, March AFB and Albuquerque Airport) in the same order:
(All imagery is via Google Earth)