I just came across a certain author, highly respected, argue thus.
Organisms evolved to adapt a mouth for the purpose of ingesting nutrition, same as insects evolved to have wings coz certain factors favoured that evolutionary trait. Well, he also argues, humans are still evolving, and even our sexual organs are still in evolution. So in the future, our sexual organs may not exxlusively only be the vijayjay and the penis...aah wharever.
Ooh mind you the author is Yuval Harari, and he's also gay! The wife to his spouse!!