[ks2048]

On the wikipedia page for "CJK Unified Ideographs Extension H", under "History"(https://en.wikipedia.org/wiki/CJK_Unified_Ideographs_Extensi...), you can find dozens of linked documents describing why someone thought they should be added.

One random example I opened (https://www.unicode.org/L2/L2017/17099-haifeng-county-uax45....) is a 9 page PDF proposing a single character used for "congee shop signs in Haifeng County".