It's not a big enough industry to support their valuation. Many companies have developed clever equipment for the film industry over the decades[1] and none has been valued at $15bn for it[2]. As an example: Panavision sold for $622M last year.
They really need to (edit: continue to) be selling to consumers. That said, I agree completely about their quality and success.
[1] - Check out some cool stuff here: https://camerarevolution.com/
[2] - Kodak might have been, once upon a time, but I can't find a breakdown of their motion picture revenue so it's hard to say.