[[SPOILERS]] Yeah, but kris can take out the soul whenever, proved at the end of ch1. They therefore choose to remain within the control of the soul. Spamton doesn't have a choice.
The dialogue in-game is just as disturbing too, almost as if there's someone crying out silently inside of spamton - a soul trapped within a puppet of a body. The ending with spamton neo means a lot more once you've realized how conscious spamton is about everything. In a way spamton is like Kris, a puppet of a body controlled by the soul of a completely different will.
this is honestly pretty sad when you think about it. Jevil was unaware of his imprisonment, he was happy and content the way he was. Though, Spamton knew everything...He knew he was trapped. But there was nothing he could do about it. Even pleading to you, the player, could do nothing to free him from his misery.