Wix may still be in the wrong, but WordPress is definitely in the wrong for removing copyright and license. IANAL but both of these companies would look awful funny in court because disregard for other people's licenses doesn't help your case when someone disregards your license.

As far as I can see the files that were originally under MIT still have their original copyright statements intact, as comments above illustrate. Which files are you alleging have had their credits removed from?