[jasonhong]

I'd say it's a combination of several factors, including:

- The designers / developers thinking that they are typical users, and that they know how things work ("You are not the user" is the phrase we repeat a lot here at CMU)

- A lack of education about how to design things (e.g., basics of perception, design patterns, basic interaction principles, conventions)

- Time and money

- A common mentality that "we can fix the UI at the end"

- Legal requirements, marketing, corporate partnerships, etc, that is all of the cruft that doesn't focus on user experience

- For popular products, a very large user base, which means legacy support (people don't like change), and different people using different features (I once heard that people only use ~20% of features in MSWord, but it's a different 20% for different people)