Eren could have some child back home. Realised he only had so long to live and asked mikasa to recommend him the best woman to start a relationship with.
Eren does have a child back home.
His name is Zeke Yeager :D
Grisha and his memories have now activated in Erens conscious ever since he went into the basement.
To Eren, speaking to his deranged grandfather probably feels like he was taking to an actual father.
And Zeke probably feels like a son as well as a brother.
Imagine you had a brother, but your memories of him are of you raising him and loving him as a son.
That's probably what Eren feels like.
And with Eren now in Marley, all current generations of Yeager family are together in one place.
Grishas senile father in the hospital.
Grisha in Erens memories.
Eren
Zeke
Add to that both Grishas and The Owls memories of "the resistance" movements to overthrow Marley also now in Erens head, as well as all the dramatic suffering their family has endured all be sure of Marley.......
Its easy to see why Eren is now there tbh.