Isn't the same true of, like, Diwali or Chinese New Year, or Eid al adha?

People make a big deal about holidays, pretty much regardless of cultural origin or economic system. And then the merchants will tend to accommodate the way people in whatever culture celebrate that.

Valentine's probably doesn't even crack the top 10 in terms of holidays that change my behavior or spending, and I say that as someone who genuinely likes to do something for my wife on Valentine's. There's the major cultural ones (Christmas, Thanksgiving, Halloween, New Year's) and then the legal ones (Memorial Day and Labor Day) that are nice to plan long weekends or barbecues around.