Too me, it's really telling a story that need tension and release. And writing music is telling a story. But that applies to everything : book, cinema, painting, architecture. If nothing happens, no change in angle, in color, in motif... You loose your audience, your public. Yes it's not an absolute rules -Their no rule in art- But it applies to most of what we see.
Let's take a paint. Imagine a hill in front, your eyes follow the shape of the hill, on top your eyes meet a blue sky with a transparent, almost inexistent cloud. You're wondering if the cloud shape is meaning more than you see. Then your eyes continue to follow the hill. That lead to a little tree at the back, that have an unexpected color, maybe it's in the shadow of the hill, [and so on...] Their we are. The painter told us a story.
To come back to music, any theme development from any master tell us a story, with... tension and release. If I imagine a music without ANY tension and release, it's a single note, constant pitch, constant volume, for 5 minutes...