My guess would be bandwidth. Every bit of bandwidth is precious, so they probably dont have the spare budget to send long audio files without obvious scientific value...
The two resectful and fun comments between 'this' comment and your comment.
I can imagine a Tumblr/Reddit re-post would be more fun, but-yes-not for the NASA suggestion box. They would have 1 diamond idea every 100k unusable ones.
I can imagine every gaming company would LOVE to have the original Mars sound in their games (e.g. "No Man's Sky").