Why do fairy tales have happy endings?

Not all do, and the good guy/gal is not always victorious. I can name several fairy stories or tales which end tragically. Pied Piper of Hamelin- an evil man gets away with abduction of a large group of children, who presumably die. Little Match Girl- dies, either of burns ( not directly suggested) or exposure to cold in the heart of the Christmas season while crowds walk by idly and are attuned to the window displays of the big stores ( it has class- struggle orientation- like the song Artificial flowers). There are others with more-or-less open endings. the reality of dysfunctional family life or, say Prince Phillipp sent to the Front in some big war- doesn"t come back alive- never happens, though it is a sort of selective villainy- but I have name two where the bad guys or bad circumstances- dominate. also, the original Little Mermaid died ( by dissolving into the water prematurely for the crime of race-mixing.