Depends where in the world you are. In the US it was popularized by Dr Kellogg to curb masturbation. He also recommended a few drops of carbolic acid applied to young girls clits to damage the nerves and avoid what he called “abnormal excitement”.

Dude was opposed to pretty much anything even vaguely resembling pleasure, he invented corn flakes as a food to be as bland and tasteless as possible. The only reason they ever became a popular breakfast cereal is because of his brother adding sugar to them despite Kelloggs objections

‘cleanliness’ and ‘looking like their father’ were later justifications after the practice had already gained traction.