[nly]

This is simply because over times systems destructure.

Some developer eventually can't be arsed to stop and _think_ for half an hour about how to solve a problem, so proposes replacing the carefully thought out DSL with a Python script.

The typical programmer does have any respect for code they didn't write themselves or what it was trying to accomplish.

[throwawaymaths]

I don't think this is the root cause. Declarative languages really paper over details in many cases, and the mapping from the declaration to the imperative execution might not be obvious. When you're on the happy path, it's amazing (if it's a good DSL: because you can be confident you haven't forgotten details, that it's systematically correct, etc). When you encounter a regression, bug, or misunderstanding, in anger, it can be very very difficult to figure out what's going on.