Let’s make a test for this:

• is it an industry you’d be forced to save if it went bankrupt?
• is it a natural monopoly, or a field that consistently concentrates to at most 1-3 companies?
• is it so important that a labour strike or shortage causes significant external impact to the economy as a whole?
• is it a foundational infrastructure with no viable alternative replacements?

If you answered yes to these questions, then you should nationalize it.

The free market can’t or won’t ever provide a better service, and there’s no viable replacement. There’s no value in it being private, in fact, it’s negative value as the corporate margin acts as a tax anyways. If you took all the corporate profit and dividends and reinvested, you would be further ahead than privately owned.