Uh, why did you post this multiple times? Once is enough.
Anyway, while it's obviously physically impossible for ANY two creatures of the same sex to produce offspring (unless you count hermaphrodites such as certain plant species or sex-changing critters like flatworms), it is unfortunate that they can't fall in love in this game. Maybe they don't want to admit being homosexuals? Maybe Tamagotchi World is extremely prejudice toward gays? ok, all silliness aside, they programmed it so same-sex tamagotchis can't mate because they don't want the whole sibling love thing going on.