Again, it isn't "providing unpaid labor to AWS". It's "problem solving and exhibiting talents to others that are in your field". It's showing you have the skill to throw such a thing together quickly. It's a resume builder. And most importantly, what you seem to be missing, it's a fun challenge to some people.
If I stretched your analogy a bit, I would say it's like seeing a body shop do a shitty job on a car, and then buying $30 worth of tools and doing a better job in an hour than they did, then posting the video to Youtube to show all your fellow car enthusiasts.