There are a number of programming languages that seem to be specifically designed for solving code-golf problems (05AB1E and Jelly immediately come to mind). Should providing a "decomposed" explanation be required, or at least strongly encouraged, as part of the answer? By '"decomposed" explanation', I mean something like my answer to this challenge.
No, it shouldn't be mandatory. But it is encouraged
Making it mandatory would cause problems, such as:
How do you draw a line between languages that require and explanation and those who don't? That's very subjective. Not everyone is familiar with Python, and not everyone finds Jelly difficult to read.
For some answers, even in "difficult" languages, the explanation is hardly necessary because the code is so simple. Again, the distinction is subjective.
On the other hand, it is already encouraged to include explanations. Answers with explanations tend to get more upvotes. This is part of the culture of the site.