This is part of ExpertCodingSkills.
Simple programming interfaces and protocols have an obvious advantage: non-PHDs can use them (or, better said, PHDs can use them). "Simple" interfaces generally enjoy a larger user base. They also tend to be more durable, lasting longer than their more complex counterparts, because complex hard-to-use interfaces are eventually subsumed by simpler interfaces that offer the same functionality.
Simple interfaces don't require reams of documentation. A few lines of text per class and method plus a few examples should be all the documentation that's required.
The authors of simple interfaces resist the temptation to satisfy every need. Basic features are provided first, and more advanced features are added later via new objects and interfaces. It's better to build complex systems by utilizing simple objects rather than altering (complicating) existing interfaces.