I think that first of all, they want their tributes to be heard.
Well technically the first works I've done for OCR were for an album which didn't have the exact same requirements as a standard OCR remix.
When I'll do it precisely to submit for OCR is gonna be another story, and the Why is simply to share what I've done. Also, the challenge of getting a Yes, which means learning production things and keep doing it, get better and better...
I think such a target is a great way to learn how to work when dealing with other people because normally, when you make music that's not OCR related, you have absolutely no guideline and limits... However, if you make a track for a game compagny, well I figure you need to craft something according to their own standards.