Its a nice portfolio project. A toy renderer (at least, when the job market wasn't so dearth) leading to a thesis or an engine programmer position at some AAA studio is a very worthwhile tradeoff.

The skillset and ontent is also just different. You don't see games on github (publicly) because they are being made for sale. Very few engine projects are serious commercial projects. I think I'd be safe to say that a commercial engine is harder than making a commercial game. Especially since Unity and Unreal have mindshare and are free to start and learn with.