It's easy to get carried away when designing new things. Adding more things means adding complexity and keeping things somewhat reusable and maintainable requires multiple layers of abstraction. This can lead to systems that aren't either and on top of that become over bloated.
It's always easy to add complexity. It doesn't really require any additional effort. Just keep adding things on top of all the previous ones. Nobody benefits from such burden.
Keeping things simple might be easy in the beginning. But as the amount of things in the system increase so does the effort of keeping things simple. I would assume the effort towards simplicity is greater than the burden form overly complicated system.
There is however a limit to the complexity of a system that can still be maintained in a working condition. At the same time the systems usability degreases ad the complexity goes up. With a perfectly simple system these should remain constant.