The government needs to take over things which are not viable for the private sector, but important for society to work.
Lets say privatisation of public transport: In countries where it is completely private, only major cities have reasonable connections. Because those are the most profitable ones. But if you want people to actually use public transport, you need to have a fine and widely spread net of connections. For that to happen either the state completely owns the public transport, or takes off financial pressure and only partially owns it.
Exactly this mechanism enables (partially) state owned organizations to run suboptimal. As explained in the example, this is a desired effect. But it also enables memes like the lazy state employee - which are at least partially true.