Which immorality has Allaah revealed the following Verse for?
And when they commit an immorality, they say, "We found our fathers doing it, and Allah has ordered us to do it." Say, "Indeed, Allah does not order immorality. Do you say about Allah that which you do not know?"
The Arabs would make Tawaaf of the Ka'bah naked.
Why did they do that?
It was an innovation they innovated.
Why did they innovate something like that?
They found their forefathers doing it because they believed it was based on the Commands of Allaah and His legislation.
What was the "logic" behind this innovation of theirs?
They said we disobey Allaah while we are in these clothes. It is not fitting that we make Tawaaf of the Ka'bah in clothes in which we have disobeyed Him.
If they were doing what their forefathers had innovated then why did they say Allaah ordered us with this?
Their forefathers innovated the practice and made it into a sunnah. They believed that Allaah wanted them [the progeny] to continue the sunnah of their forefathers, and so they said He ordered us.
So, in a nutshell their forefathers innovated an innovation. They thought it was based on the legislation of Allaah and would get them close to Allaah. The progeny continued on the practice because they believed Allaah wanted this innovation to persist for generations. Is this correct?
Yes, this is correct. That is how innovations work. The innovator innovates an innovation. He believes he based the innovation on the Command of Allaah. Then he teaches his children the innovation. They in turn teach their children and the evil practice continues for generations.