Exactly! Five points, Keiichi, that's more than I expected out of you!

[A nod and then she sets off]

Looking at it objectively, we have dozens upon dozens of Earths which all have this same celebration across a ton of different cultures. Given the alternate history in mind, and the fact that some non-Earth worlds have it too, it becomes entirely probable that there's some entity or at least a slider-time traveler who is manipulating an idealized image of what "love" is for people!