This seems incredibly narrow-minded, it is 100% possible for a couple to realize their dynamic as two people just doesn't work as well in a romantic relationship as it does platonically, and if both parties are emotionally mature enough with it, they can absolutely part ways and still maintain a healthy ordinary friendship post courting.

Asserting that such a phenomenon isn't "how reality works" seems like a weird projection of whatever personal expectations and hang-ups you have about how relationships work.