Many are convinced that paying the workers, the lobbyists, shareholders, board of directors, and contract overhead is cheaper than just paying the workers directly.
I've been investigating why people think this for years. I've read a number of books, listened to lectures, went to proseminars in economics at UC schools, took some classes ...
Recently, I've become increasingly convinced it's actually just a giant hustle. It's an elaborate ploy that makes people money. Things like Demand Theory or the Efficient Market Hypothesis are modern astrology psuedo-sciences with real world evidence that's incidental or statistically insignificant at best.
This is especially true for the second-order implications like privatization.
There's no persuasive material evidence of the purported theory that privatization is more efficient. The most favorable evidence from the supporters (for instance, Megaprojects and Risk: An Anatomy of Ambition by Bent Flyvbjerg he has 3 more on the topic) say that private and public projects are about the same. They go over budget about the same and fail about the same.
Other more critical quantitative studies show dramatically better outcomes for publicly controlled systems - look at Oxfam studies for instance.
There's also a lot of evidence that the private systems however mint millionaires who make an absolute killing off the taxpayer.
Just like 500 years ago how religious people controlled the narrative and set up the rules of society and "laws of nature" to basically be giant money trees for them, there's a new class of people who have done the same thing.
Recently I've been studying where this economic school originated from (essentially Chicago Boys style) and what was driving it. I haven't found any serious scholarly work on it beyond things written by journalists.
The journalists track it to various organizations that formed after the new deal (each author has a different boogeyman) but the narrative is essentially the same: create think tanks, pack the colleges with favorable people, witch hunt the critics through red/left/whatever baiting, silence alternative views, create a media through movies, news, and television that support this view and so on.
Not because it's accurate, right, or correct - but because it makes them a lot of cash. The narrative actually changes.
Groups like the Heritage foundation or the American Enterprise Institute move their goalposts constantly over the years and defend it on supposedly principled economic grounds.
The problem is that you can often find, such as in healthcare, documents where they make multiple fundamentally contradictory arguments because the underlying market mechanics they defend are pliable devices of convenience to push the agenda of making private capital and that's literally it.
There's nothing deeper, nothing more fundamental. It's a giant hustle.