That's covered in the article, my bullet points were just an attempt at a summary.

Briefly, it doesn't work like that. Interviewing developers is very unintuitive. Many reasonable expectations are violated. There are lots of people who can talk very well and will appear to have a good understanding of programming, up until the point that you ask them to write a program (any program) at which point they can't even start. If you don't force candidates to write an actual working program you will pretty quickly hire people who just can't do it, and then have to fire them later. Yes this sounds totally wrong, everyone struggles with this fact at first. It's sort of like the Matrix. Nobody can be told what interviewing is like from the employer's perspective. You have to see it for yourself.