The eschaton will devour the people who “join them” just as fast as the people who fight it.
As Jack T. Chick said, "No one can save you. We will all be eaten."[1] But isn't the real goal to be eaten first, so you can miss out on all that noisy screaming and awful mess?
Eschatons have a solid track record of never showing up when invited, so there's that.
1. https://www.reddit.com/r/Cthulhu/comments/1m9uxmp/who_will_b...