I think people are leaving MC due to more of their interest in Winx Club waning then anything that has to do with the website.
Even with the up to the minute spoilers and discussions it is hard to keep interest in a show that no longer shows in your country.
Take the Avatar: The Last Airbender community. Activity went WAY down after the series ended but with the new movie out activity has picked up in the fandom.
I know the series hasn’t ended with the confirmation of a second movie and a 5th season but USA and Canada no longer gets the show which feels like the series ended at season 3.
Maybe if the rights are taken back from 4Kids, given to another company (like it has been talked about), and the show starts to air in the USA and Canada activity will no doubt pick up. Until then lets just hope not to many people loose interest in Winx Club.
Reason for edit: removed the C word