But it's not. There's considerable spread in the price of music depending on the quality, specificity, popularity, and licensability* of what you want to buy.
* up to a particular number of copies made, or with restrictions on sublicensing or other contractual factors.
You make a new film (which includes the entire range of things from Hollywood films, to pro-Youtubers to films you share with a couple of people).
For music you can
1) Get custom music written specifically for your film. This is usually expensive (unless you do it yourself, or know someone to do it for you) but has the advantage (if done well) of matching exactly what you want for your film
2) Find an existing piece of music and license it. This has variable costs (or maybe free), but won't be written specifically for your film and possibly will also be used elsewhere.
3) Use "template" music included in whatever software tool you are using.
AI-generated music has the advantage of (1) but the cost structure of (3).
It'll be a long time before it is useful for Hollywood films. But for Youtubers it is a completely different story.
At the moment the per-unit cost of per film is constant. If software "composes" the music then the per-unit cost drops with each additional user.
That's the radical thing.