If you want to know why only the reboot is getting retconned and not seasons 5 and 6, well two reasons. First is that I can clearly tell that the reboot takes place in an alternate timeline, but seasons 5 and 6 take place in the same timeline as the original. Second, as much as I hate some episodes from seasons 5 and 6, retconning them would lead to some missed opportunities for some ideas for episodes I have in mind for my idea of a 2nd reboot, which takes place after the 2nd movie.