It's possible only those who were prepared to awaken were included in the simulation. However, our eldest brother is still sleeping.

If we're lucky, he'll stay that way.

[He'd probably prefer it. Unless their gracious overlords find a way to keep their bodies from rotting... but considering the state of Mephisto's own body right now, that doesn't seem to be the case just yet. He's lucky only Amaimon had to face the humiliation of stripping down to his skivvies in dreamland, seeing as he preferred to keep his current condition to himself.]