Because private charities rely on someone making an affirmative choice to give them money. In theory, if they are corrupt or incompetent enough the flow of money dries up.

If the government is corrupt or incompetent, people get angry at them and then ... nothing changes. The flow of money isn't stopping, in fact the most likely outcome is their budgets keep going up year after year.

That sounds the exact opposite really - one is answerable to voters and while the other is capable of acting like a MLM organization that does nothing for the nominal cause except marketting.

Look at the old institutional system - they had loads of bad PR and were killed off - there may have been cynical reasons for doing so but it was held accountable.

Then look at all of the private "reparative therapy" and other opposite of helpful private organizations still around.

Not that being able to opt out isn't a big advantage but private bad ones can stick around way longer than public ones.

But then you have to accept a situation where only the people who have money (or those on their payroll) can implement policy. You might improve the efficiency that way but it doesn't sound much better to me, especially in communities with a history of discrimination.