I don't understand why you presume it's a need to defend and justify it to others. Getting a PhD from MIT isn't exactly a walk in the park, I imagine the person got it BECAUSE of a pleasure to tackle complicated problems in the first place.

If I really enjoy dealing with complexity and you give me something really simple to do, well I'm gonna go ahead and have some fun with it. It's not a matter of justifying, it's just that simple stuff is boring to somebody who enjoys complexity.