Finney did an interview right before his death while he new perfectly well this was be his last interview. He had no reason to not reveal if he was SN, moreover, he told he wasn't Satoshi
If you were him... will you protect your family interest, he may likely does not want anyone to disturb his family codes. He's a wise man.
This reminds me of a story where a black politician man built a company in the name of a white man to free himself off corruption allegation. He planned with the white man and used the white name on the documents and handed over to him. guess what? the white man handed all documents to his son killed himself, when the black man came for him documents, the son won the case and claim the company.