UI development is the hard part. And it’s not the last step, it’s the first step. In my estimation, the difference between:
- software that performs function X; and
- software that performs function X, with an intuitive well-designed user interface
isn’t just a little bit of extra work. It’s not even twice the work. It’s an entire order of magnitude more work. Developing software with a good UI requires both aptitude and a lot of hard work.