A member from the ‘Attack on Titan’ fan page on Facebook came up with a theory that sounds ridiculous but knowing the show ‘Attack on Titan’ it could be true.

Pinku Ichikawa brought up the scenario about Ymir’s three pigs from 2,000 years ago. They were three pigs (Grisha, Zeke, and Eren), but only one escaped (Eren). The other two (Grisha and Zeke) stayed even after Ymir opened the pig pen, This means they didn’t want Freedom enough. Grisha and Zeke’s titan are chubby, while Eren’s titan is fit because he escaped and ran for his life. Just one pig escaped. Ymir freed Eren, now he has returned the favor. “To You, 2000 Years From Now”