Alex, in both examples you list, the Army Air Force members were on detached service (DS) from a parent USAAF unit and the parent unit did the MACR. So the AAF did do MACRs in some circumstances involving RAF planes and crews. Thanks for the correction. I am thinking that in Roberts case, he was not yet officially in any AAF unit, so there was no "parent" unit to take-on the responsibility.
A little on Ray Jay Gile, involved in MACR 8712.
https://www.wikitree.com/wiki/Gile-59