For quite some years, LEGO has been releasing sets around different holydays. As far as I can trace back, this started in 2010. This seems to be the first year where the seasonal sets (excluding Monthly Mini Model Builds, I’m looking at retail sets) where not only for Christmas. It started out with small polybag builds, but they slowly became bigger. In 2018, Seasonal sets in the form of Brickheadz were introduced, going on into 2019 and 2020.