The reason we occasionally delete answers is that the system will automatically redirect people from Google to the fully-answered questions. We don't do it all the time. Examples include answers that have very specific information for the asker (but it's duplicate nevertheless), or where a merge is suitable.

In this case the deleted answer just points to your other answer. Leaving it there makes the newer question worse because it would stop an automatic redirect.

The reason we occasionally delete answers on duplicate-closed questions is that the system will automatically redirect people from Google to the fully-answered question. This has the obvious benefit that they get access to the best version of the question and its answers. 

We don't do it all the time. Examples include answers that have very specific information for the asker (but it's duplicate nevertheless), or where a merge is suitable (and you're answer is moved over).

In this particular case the deleted answer just points to your other answer. Leaving it there makes the newer question worse because it would stop an automatic redirect.