Bloodline shackles.
This was the reason why Eliza's clan had decided to come to Anfang, a seemingly barren world that lacked Ranking resources for the high-ranking entities.
These bloodline shackles had forced the ancestors of House Samael to leave their home in Labh Salem and find their footing in the Land of the Faithless.
Eliza didn't want to subject herself to the same form of bloodline shackles after leaving Anfang.
Achieving the bloodline evolution was her chance to gain complete freedom. A form of freedom that would not be blemished by the so-called shackles even after she steps foot outside Anfang.
If it weren't for this reason, Eliza would have no issue releasing Reen into Eren's custody and concluding the deal they had struck a decade ago. They could have parted ways and achieved their own goals after successfully running away from their siege.
