(((((( Disclaimer: I'm American))))I think it's a pinterest and IG thing. Influencers have to stay fresh and interesting somehow, so they are constantly changing their decor. Plus, more swipe ups!
Also consumerism plays a huge role. Everything in America has gotten bigger and more expensive. Every holiday has turned into a giant money making scheme and Americans were just the first to fall for the scheme. Now with the help of IG and influencers it's spreading all over the place.
There are home decore influencers who buy all brand new Christmas decorations every single year! That is just crazy. I must admit I love to decorate for all the holidays but I only buy things on clearance after the holidays and use the same stuff year after year. I think ppl from other countries would be surprised at how much Americans love decorating for holidays.