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.
To clarify, I'm not saying over-engineering is a good thing. I'm saying there's a mismatch between the complexity of the problem and the desires/personality of the person having to solve it. Give the simple problem to people who valor elegance, minimalism, simplicity, and keep the MIT PhD for rocket surgery and stuff.
This is what happens when you hire someone that's overqualified for a job, I guess. :) People in that situation need to find work that will satisfy their thirst for complexity. They are making trouble for themselves and others, otherwise.
"it's just that simple stuff is boring to somebody who enjoys complexity."
This doesn't work very well with business. Sometimes, you just need the simple solution.
It's also the reason why many startups never get off the ground. I'm guilty of it myself, but I have learned over the years to not over-engineer something until it's really needed.
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.