why don't they cite authority under 6.302-1 (a) (ii), which says the same thing but without the limitation to DoD, NASA and the Coast Guard?
6.302-1 -- Only One Responsible Source and No Other Supplies or Services Will Satisfy Agency Requirements.
(a) Authority.
...
(2) When the supplies or services required by the agency are available from only one responsible source, or, for DOD, NASA, and the Coast Guard, from only one or a limited number of responsible sources, and no other type of supplies or services will satisfy agency requirements, full and open competition need not be provided for.
...
(ii) Supplies may be deemed to be available only from the original source in the case of a follow-on contract for the continued development or production of a major system or highly specialized equipment, including major components thereof, when it is likely that award to any other source would result in --
(A) Substantial duplication of cost to the Government that is not expected to be recovered through competition, or
(B ) Unacceptable delays in fulfilling the agency?s requirements. (See 10 U.S.C. 2304(d)(1)(B ) or 41 U.S.C. 253 (d)(1)(B ).)