This style of music didn't arise in movies and get mimicked in symphonies, it's the other way around - this symphonic piece wasn't written to sound like a movie score, it's that movie scores are often written to sound like symphonic music.

Instrumentation is surely part of it. Movie scores are often performed by a full symphony to give a rich palette of sounds and textures to work with, and tend be mainly instrumental as lyrics could conflict with dialogue. Symphonic music also lends itself well to original compositions that blend into the scenes of the movie, as opposed to other styles like pop music which will tend to draw more attention to the artist or music itself, and which cannot be as easily modified to fit the timing or emotional beats of the scene.

This style of music didn't arise in movies and get mimicked in symphonies, it's the other way around - this symphonic piece wasn't written to sound like a movie score, it's that movie scores are often written to sound like symphonic music.

Instrumentation is surely part of it. Movie scores are often performed by a full symphony to give a rich palette of sounds and textures to work with, and tend be mainly instrumental as lyrics could conflict with dialogue. Symphonic music also lends itself well to original compositions that blend into the scenes of the movie, as opposed to other styles like pop music which will tend to draw more attention to the artist or music itself, and which cannot be as easily modified to fit the timing or emotional beats of the scene. Other styles of music or instrumentation may also evoke and contribute to a particular setting, like electronic instruments in futuristic settings or traditional instruments in fantasy settings.