[aidenn0]

Kanji in Japanese are sorted by writing them out phonetically in Kana and then sorting by the kana.

English speakers don't expect names to be sorted by IPA because most English speakers don't know IPA, but all Japanese speakers do know the kana.

The fact that they are sorted as-if written in kana means that the exact same written character will be sorted differently according to context. For "not names" we actually do have fairly good algorithms for determining the pronunciation of Kanji, but for many names there is literally no way to know how to pronounce them without asking.