The problem is that changi deal with many luggage everyday. And the luggage tag of your luggage might be missing. Thus it will take times for them to look/sort out.

it might be mixed together with some other luggage with missing tag. I won’t know the figures but it should be quite a big amount. Imagine having to go through the pile of luggage 1 by 1 to try to look for it is not easy task esp if luggage tag is gone.