Well, if you read that article down to the end, it said that Halloween is actually more popular. More people celebrate Halloween, but those who do celebrate Valentine's are spending more money on it than the Halloween revelers are spending.
I can understand this. If you are thrifty, you can decorate for Halloween on a shoestring. Heck, one of my favorite decorations is a set of "ghost lights" I made from plastic milk jugs, using a Sharpie pen for drawing the faces and a string of clear Christmas lights. Not much expense involved there! But if you are going to buy something for your honey on Valentine's Day, you had better spend more than you would spend on a trio of plastic milk jugs!
And just consider how many people get engaged on Valentine's. Think of how much an engagement ring costs.