They want more of your money. They will monetize you as much as they can. You're just a well-supported, paying product.
The default reason some feature doesn't exist is simply because no one bothered to make it. Maybe they don't think there's a big demand from their users to disable shorts completely.
When a pusher gives you some free drugs, they are not taking into account whether you want to be addicted to drugs. Not part of the business model.
They make all sorts of money doing that, but they get upset when people say Google is “selling” the data.
My guess is they know exactly what users are doing with the app and website, and know that people use shorts more often than we think.
This is one of their prime products, and they're Google, the biggest surveillance company on the planet. Of course they know how users interact with their service.