Because if they aren't, they are unsustainable. It's good to have self-sustainable industries rather than endless businesses (state owned or not) forever sucking on the public teet.
> It's good to have self-sustainable industries...
There's no such thing as a 'self-sustaining industry'.
They all rely on common transportation infrastructure which they use to ship their materials and goods around and get their employees to work. They all rely on a predictable and fair marketplace whose fairness is governed by the state, and they all rely on people not coming and burning their premises down because they're protected by the state!
