In fact, changing Shaggy's diet was a condition to get Kasem to voice the character again. Kasem quit in the 1990s and was replaced by Billy West and Scott Innes when he refused to voice Shaggy in a Burger King commercial. So when the producers of What's New, Scooby Doo? tried to get Casey Kasem back, he insisted on the change to Shaggy being made.

https://screenrant.com/scooby-doo-shaggy-vegetarian-casey-kasem-true-story/

Shout out to a real one