The thing is here, is that Yamato has been shackled to Wano for over 20 years without being able to leave because of her father. This isn't some instance where she has been free to come and go from Wano as she pleases. The Country has been her prison for over 20 years. Oden broke the rules of the Country and left of his own accord, where as Yamato was forced to stay in the Country, unable to leave because of her father. She's been desiring that freedom, and being able to sail the open seas for over 20 years, yet unable to.
One Piece is all about breaking oppression, and symbolizing freedom. Wano opening it's borders is a step in that direction for not only the citizens, but Kaido being defeated is a step in that direction for Yamato. It'd be a convoluted twist if for some reason she decided to embrace this new role of some kind of guardian because of eating a devil fruit that thematically shackles her to that fate, and goes against one of the core concepts of the story. Freedom. Even if she makes that decision to stay, it would feel like that fate was set in stone the moment she ate that devil fruit.