Hi,
From your post, at least you do sound like you have done some research on SIA's fleets... and that is a good thing. There are many other interviewees who have absolutely no idea what is the physical difference between a 777 and a 747.
Even so, there are some fellow pilots that I know who lack "passion" in the job. Some are in it for the money, sadly... but hey, there's all sorts of people everywhere.
Dun be disheartened about your lack of success for the interview. This goes out to the rest of the "rejectees" too. There is a pilot I know who went for the first interview SEVEN (7) times, and now, he is a Captain. So, try again.
Good luck for your next interview!