> You should be able to install your own operating system

So you draw the line between the bootloader and the OS. Other people draw the line between the OS and applications. Most (nearly all) people can't write either, so for them it is just part of the device.

> you don't get to tell them how theirs should operate.

I paid for it, and I allow it to be legal in the jurisdiction I (partly) control. So it is not only theirs anymore.