I noticed the same thing when interviewing people. Answering why a decision was made would always trip people up, but it's far more revealing than any demo project can be. It doesn't matter, to me, whether the solution was right or wrong, but more the "why" that got you there and how it will get you to where you need to go. You can't problem solve effectively without understanding the reasons you're making the decisions you are.

The same follows for patterns, I think. If you haven't thought about it critically and really done the work to understand the "why" (being told the "why" is not enough) you're going to struggle and mostly fail to implement it properly are in the appropriate situations.