If you press the delete button and press OK the next prompt you'll get is:
Sorry, this question has answers and cannot be deleted; flag it for moderator attention instead.
I can't speak for the moderators (that flag would be handled by diamond moderators) but would guess they'd be hesistant to delete it because while it's been solved for you it might be useful to future visitors. The view count of 717 over the past year isn't huge but I've seen questions with a much lower view count that have helped me.
In fact only today I searched for something that threw up a StackOverflow page that was over two years old and didn't have any votes on the question or the answer that helped me so I upvoted both. That involved a technology pretty much obsolete for close to ten years which is probably why it wasn't popular, but it gave me a quick solution to maintaining some legacy code.