"He came up during a time when everything in jazz was big the bands, the sounds, the opportunities, the personalities, the coverage and this formed and marked him. Everything about his playing his tone, vibrato, ideas, emotion was equally big, he was just huge. But after The War and with the advent of bebop, the music got smaller the bands, the sounds, the emotion, personalities everything became paler, cooler. Harris did a better job than Norma Desmond in adapting to these changes, but the bigness of his overall conception still stood out and didnt fit into the newer, smaller surroundings, hastening his trip to the sidelines." https://wallacebass.com/bill-harris-trombone-surrealist/
Big bands gave way to small groups.
It's reaching to say that in movies, the studios were big and even had their own theaters. This gave way too to independents.