They would be losing money without overpriced repairs. That's why they lobby so hard against right to repair.
Even with some kind of right to repair it still seems they're trying to keep you hooked on their resources.
But as you said, service manual + schematics would be great for some people. But companies will fight tooth and nail against it. They lose control over obsoleting older products.
same reason car dealerships want you to only go to them for maintenance
Which is a huge problem when you live in bum fuck nowhere like many farmers.