I'm not sure if I saw it on a Wikipedia page that tried to explain it or if I saw it in the BoyChat thread, but one proffered logic was to prevent disruptions.

It's to cut down on "attacking the messenger" in discussions about content.

Imagine the different tones of discussion this would have:

Scenario 1, davidd does not identify himself as a racist on his Talk page:
dduke: I just edited the KKK article to give it a more NPV. It was becoming a bit bashing.
{little or no discussion follows}

Scenario 2, davidd identifies himself as a racist on his talk page
dduke: I just edited the KKK article to give it a more NPV. It was becoming a bit bashing.
{lots of replies calling him a racist and a revert war ensues}

David Duke was a racist Louisiana politician of the '90s.