I think it's also because redheads also tend to not be the main protagonist (not all the time, see how they're fucking up The Little Mermaid). Easy way to add a minority cookie for a secondary character or villain.

Some are, some aren't but it does heavily affect secondary characters like Lex Luthor, Jimmy Olsen, Heimdall, etc.

Merida from Brave would be one as are Annie and Ariel pre wokewash. Some others are protagonists of their own series, like Hawkgirl or Wally West but they are themselves derivatives of original characters such as Hawkman and the previous Flash characters respectively.

I say cookie because they clearly don't give a fuck about actual diversity when we've had like 30 redheaded characters get swapped for black characters. Asians? Native Americans? What the fuck are those?

Despite making up 13% of the population... [in Scotland], redheads are 100% wokewashed in modern day casting.