Because gamefreak keeps avoiding talking about Pokesex. No one in the game is smart enough to observe two pokemon in a day care center (What do these Poke Profs get paid for, even?) and it's a straight up mystery as to how baby pokemon happen.
A stork Pokemon would get rid of Pokesex and relieve everyone in game of looking like idiots.
Then they should make it a tooth fairy type. --- Black 2 FC:0519 5089 8733