that's just sunk cost fallacy. The icons are also publicly available and can be used on projects conforming to the Apple branding, so it's not truly a waste.
If anything, the waste would have arguably been putting people to work on a feature that needed to get removed in the first place. If there's any post-mortem to be done, it's "why did this get released in the first place, and how do we make sure we don't spent time on something like it again?"