My completely uninformed guess is that this project was in the works for years, and it's not simple to postpone. For example, they would have mapped out where the moon was going to be, what its rotation would look like, how they were going to approach, etc.

Perhaps this is easy to re-calculate for another year, but when you're dealing with narrow tolerances for error, maybe there's a heavy bias to just stick to the plan? They probably were also hoping for a PR win, which obviously backfired in this case.