Because any time a government actually does try to rout corruption, every corrupt government circles the wagons and begins to strangle them to death.

You in fact do need a strong authority to enforce morals and remove those who disobey. If you try to leave it to a "small government" or the public, then the degenerates will team up and gradually overpower them. Normies just want to be comfortable over anything else, and will gladly choose what they think is the "lesser evil" to accomplish that.