It surprises me, talking to folks who are new to screenwriting, how many of them don't have a movie in their head. If you don't see a film, how are you going to make anyone else see it? They are telling a story, not creating a film. This often becomes clear if you ask them - what is character y doing while x and z are talking here? Or some other detail about something they put in the room and then left alone. They aren't *seeing* the scene.
Of course, I've always imagined somewhat cinematically. Even my most abstract poems (with the exception of a couple of grad-school literary cut-up experiments) run in my head as a short film. And I can tell you what every detail of each frame looks like.
Then there's the other sticking point - once you have the movie in your head, knowing how much to put down on paper to evoke those images in another person's head. Most of us have been told enough times not to overwrite that it's less common to see an overly florid screenplay than one which chooses such generic descriptions/dialogue that they flatten out and the flavor of the imagined story is lost. You can do a lot with the flavor of the language, rather than endless description - something I learned from poetry.
Yes, the language of a screenplay is stripped down, basic and straight-forward. That doesn't mean it can't be evocative. Your hero can walk down a wet street, or they can splash through the wet grime of rain-slicked asphalt.
My signature on Triggerstreet is: "Don't tell me the moon is shining; show me the glint of light on broken glass..." (Chekhov) and it illustrated perfectly what I mean. The moon may be shining, but what we see is the glint of light...and that piece of glass can add to a threatening or a down-trodden tone, depending on context.
Every word matters, every word is a chance to evoke the movie you see, in your reader's head.