Most people from Hunan moved here from Jiangxi. Why do only a few areas of Hunan dialect belong to Jiangxi language family?

Hunan is dominated by immigrants, Jiangxi is the largest, and there are a large number of immigrants from the Central Plains, as well as Fujian, Guangdong, Anhui, Jiangsu, Zhejiang and other places. As a result of multi-ethnic integration, Hunan dialect contains elements of other dialects in China, so many dialects in Hunan retain elements of Gan dialect, Cantonese, Hakka dialect, Minnan dialect, Jiangsu and Zhejiang dialect and Wu dialect. The ethnic integration has resulted in the diversity of Hunan dialects, rather than a single Gan dialect system.