I suspect calling Mayday is unpopular with some US Pilots because it's imagined to be unpopular with Legal, Marketing,
PR, Chief Pilot and the Safety dept....
. . . and anyway they never lost two engines in training so its surely going to be called over-dramatic on the ground.. I mean if Apollo 11 didn't call Mayday who would
Also mentally minimising a developing bad situation is a basic human instinct which sometimes helps and sometimes doesn't - making it tricky to train out