They were trying to conceal any association with the very dubious "old lives" before the book, not for any literary reasons.
Quite difficult these days, as Chloe H has proved. My gt gt grandfather (1870s) disappeared after the birth of his daughter and much digging doing the family history showed that she was taken in and brought up by his sister, her mother is still a mystery, not married of course.
I stumbled across him a few years ago, 200+ miles away, census decades later, married. With a singular and frankly Jeremy Kyle like lack of taste, a daughter of the marriage had the same name as Gt Gran. Ratbag.
You'd find it more difficult to vanish now, Jeremiah 😂
ETA there was a family story that her family were "posher" than his. It wouldn't be hard.