Sorry Mustrum, but those two holidays originally had a religious contextes.
Valentines day was named after a one of two Christian Martyrs (there were two Saint Valentines)... It's unknown how it got attributed to romance during the 14th century. However, I'm pretty sure it had to do with relic based superstition (If you go to Saint Valentines church on so-and-so and kiss his (thigh) bone you will become a virile).
Mother's day has pagan roots and basically is a celebration of a pantheon's mother goddess.
If anything I think you should have asked "How did International Talk Like A Pirate Day get introduced?" since that's the best analogy to what you were saying.
