SQ is very restrictive on which booking classes give bonus points. Earlier they even had a bizarre rule that stated that if you were booked in different booking classes on a multileg intinerary, you did not get points for any legs if one of the legs was in a non-earning class. You could thus theoretically fly full-fare Y (i.e. booking class Y) from Europe to Singapore and not get any points for that, because the short connecting flight to Denpasar was in a non-earning class. This particular nonsense ended a couple of years ago, but they are still very stingy when awarding points, at least outside their own program. Basically: they want your money, but they don't like frequent fliers. Seeing that some probably choose SQ because they are *A this tastes of bait-and-switch.