Which she can do without joining the strawhats, hell she doesn't even need to leave Wano to do that now that Kaido's reign of terror is gone. Fact is, Yamato doesn't have any grand moment waiting for her in the next 3-4 years until the series ends, since her dream technically is already realized, which cannot be said for any of the other strawhats. Yamato is not going to explore the seas and have a grand adventure by going to 2 islands then shutting shop.