Or may be sex activities exist... but just for .... fun?
Not for procreation?
https://www.youtube.com/watch?v=JxxNvfVfDB0Maybe. I mean a common backstory is that the Mario Bros. were originally from Brooklyn, Earth and on the job they found a warp pipe to the Mushroom Kingdom where they decided to stay. Sex maybe a foreign concept to them. Kinda like the movie Pleasentville. It could be possible there is some sort of
suppression field throughout the world of the Mushroom Kingdom forcing storks to be the only means of reproduction for the human residents that live there.
But after seeing New Donk City and the fact Pauline is the mayor, I'm starting to think Mario and Luigi are actually from New Donk City and that NDC is on the same world as the Mushroom Kingdom, meaning the same laws apply there.
And ever since the introduction of the Super Crown, some fans theories that the mushroom people are actually an eusocial race similar to bees. Princess Peach was perhaps once a Toadette and was given the Super Crown because she was chosen to rule over them. And if she is no longer fit to rule a new toadette will take her place.