[Lastodon]

It's the name, IMO/IME. Mutton as a name is unappetising. "Mutt" brings dogs to mind, and the "un" sound at the end makes it sound lumpy and gross.

A lot of people don't even know that mutton is sheep, they'll say stuff like "I thought Lamb was sheep!" Etc

And before you dismiss this idea I would like to draw your attention to the multibillion dollar market that is marketing.