Why? To have a reasonable measure for the intelligence of their children.
Heard of regression to the mean? An unusually smart person from a background of dumb hick proles, is not going to have kids nearly as smart as they are.
People understand this at a genetic level when picking out mates. “Meet the family” before you decide to keep the girl/guy.
Yeah, rule numero uno of the internet is to remain ANON as much as possible.