Creeping Featuritis
Most software gradually accretes more and more functionality, making it difficult to learn.

Often the first implementation of an idea is simple, while further implemenattions are progressively more and more complex (see

This is certainly the case with wiki software. The original wiki at is one of the simplest (and most elegant and best) wikis ever developed. Its successors are almost all more complicated, sometimes for good reasons but often for bad reasons or no reasons.