

Mom’s side of the family is Catholic and my dad’s side is super reserved, so I got nothing. Anything I know comes from school health classes (which were actually really informative) and the internet.
My mom also believes that this sort of thing shouldn’t be taught in schools (at all) because it should be up to the parents to decide what their kids should know about the subject. She also says that her parents never taught her anything.
My understanding is that it’s related to the decline of three and four engine planes. Originally airlines preferred them over two engined planes because they were safer, had greater range, and could carry more passengers. On the other hand, they were more expensive to operate due to requiring more maintenance and fuel. Additionally, these planes were larger and couldn’t get into places that smaller twinjets could. Eventually technology improved to the point that the (literal) costs of more engines began to outweigh the benefits to airlines. These days most passenger airlines only operate twinjets and the remaining tri- and quadjets are relegated to cargo.