It gets the point across using the least number of syllables. People tend to think of screenplays the way they think of novels. In truth writing a script is much more like writing poetry. The form and structure are paramount, and the goal is to convey as much information as possible in as compact a form as possible. Not only does every word count, every syllable counts.
Song lyrics are one form of poetry.
I prefer to think of screenwriting as song writing. Mary's dress waves. Like a vision she dances across the porch as the radio plays. But it reads quite well as a descriptive passage. In the end, stylistically, the screenwriter is free to do whatever works to effectively convey the intent of the scene.