I can give you an example based on two failed national airlines I experienced for years: Italy's Alitalia and Hungary's Malév.

Customers hated them. They were top examples of when public management fails. They were expensive for the customers and costed the tax payers billions to be kept alive, and basically everyone rejoiced when they were let go (Alitalia being reborn as ITA Airways and effectively operated by Lufthansa, Malev just disappeared).

The problem with state run enterprises is that the accountability to voters is very removed. You elect parliament and government which chooses some administrator at random times which chooses some managers etc..

It's not impossible to do well (many state run companies are fine!) but it's hardly a guarantee.