A late cancellation spends part of the preparation somebody else already completed.

Cancelling late does not return the day to how it was. The food is bought, the afternoon was kept clear, the room was tidied, the other invitation was declined: all of that has already been spent, and calling it off only stops what remains. The person cancelling sees a plan that did not happen; the person cancelled on sees hours that went somewhere. Both are honest views, and they are not the same size.

When you have to pull out, say what you know as early as you know it. If it is very late, acknowledging the preparation directly does more good than a long explanation.