There is a lot to be said for understanding things from first principles, but not everyone wants to go that low. Not everyone is that nerdy or maybe hasn't the time or motivation.

The other issue is that not everyone learns well from the bottom up. I believe that top down is a much better way of learning anything, and lets you progressively get closer to first principles while not discouraging learners with a steep difficulty curve. But unfortunately is an approach that is seldom facilitated by anyone.