The primary thing about the changes in prices is the market. I think the following, on Christmas day, is different each time because of the investor's actions. Like how they would be in the holidays? Maybe in 2020, since there are no vacations or the pandemic is still rampant, it has increased in price because the money has nowhere to go. For 2021 however, the biggest decrease, probably because a lot of people already wanted to go on vacation or some sort. I believe that's the case and cannot classify how the investors are during the times.
Christmas is when people go with holidays, hang out with friends, meet their family members and it's special time each year. They will be less actively on cryptocurrency market even they can do it with mobile devices and Internet connection.
Whales and market makers will take advantage of Christmas and other holidays to dump the market. Usually they will go dumping the market than pumping it but this year is special and it raises a very uncertain big question.
Will the market be dumped or will it be pumped because of SEC decision on Bitcoin Spot ETF applications in next 2 weeks?
If it is in another year, I bet on dump but this year, even I think there are many reasons for Bitcoin to be dumped, SEC decision is a big uncertainty.