Well you're using THEIR network.
So my phone is using their network to pass data, pretty sure I've paid them for that service.
It's my business if I want to connect my laptop, or my 10 friends' laptops to my phone. Especially when enabling that feature is nothing but a menu setting on the phone which they think they should have control over somehow.
It's like Ford dictating that I have to pay for more than one passenger when there are clearly three unoccupied seats in the back.
Everything about it is their business. Bandwidth is a finite resource.
That's like saying "What business is it of the electric company if I turn on a 10GW load during peak hours?"
Bandwidth is not finite in the same way as electricity.
To generate electricity you need to burn more coal, react more uranium or dam more rivers. We can eventually run out of coal, uranium and rivers.
To open more bandwidth, the carrier has to upgrade their network or stop
massively overselling and committing to unrealistic speeds. The only restriction on bandwidth is how many billions of dollars profit the carrier wants this quarter.