I don't know if this is post-hoc justification, but I see myself as somebody who wants to know what everything is and how everything works - so to me, re-implementing (and always failing to take it to completion) is the means to an end. I think I spent the first 25 years of my life studying, so learning has become the goal itself. Work is there to provide funds to support me while I learn. Re-implementing the basics of something is a terrific tool for learning how it works.