Of course the Klan also flies the US flag.

Culturally in the rural south, a lot goes into convincing as many people as possible that the civil war had little to do with racism and instead it was about the elite northerners vaguely bossing the poor southerners around.

As a consequence, they get that flag flown by a fair number of oblivious people that either worship some idealized vision of the antebellum south or just in general people saying "being a rebel is cool".

Like Dukes of Hazard fans largely treated it as a symbol of generic righteous rebellion rather than referring to the core principles of the conflict that created the flag.