in SIA's case, they have said it couple of years back as "intelligent misuse" of aircraft ie 777 and even way before that on the use of its 744s for short hauls, including the really short hop of 35 min flying time between SIN and KUL vv.
This arrangement of using the 777 have made it redundant for SQ to purchase medium range aircraft (after retiring its A310s) just for their relative short-hauls ie between SIN, KUL, BKK and JKT.