Poorly-Aged Franchise

Not to be confused with an illness that turns your skin yellow and gives you an overbite.

A somewhat uncommon condition that causes franchises to lose sight of what made them so likable when they were new, therefore throwing them into a Downward Spiral until their audience either massively complains about the franchise or gives up on it entirely. This UnTrash gets its name from an obvious source. Once a franchise is infected with Simpsons' Disease, it normally spells death for that franchise as this UnTrash causes it to either be cancelled by its creators or become a Zombie Franchise if it's continued to be added on to with new installations. Simpsons' Disease can infect franchises much easier if they've been rebooted or given unwanted sequels.