bitcoin slowly went down this year, from almost 20k USD last December and went down at a significant price
what might be the reason why bitcoin's price is going down?
what are the major things that can greatly influence bitcoin?
answers would be fully appreciated

There is nothing special happening, the price went up really fast and logic dictates the price will have to go down very fast as well, the price went down a little bit lower than I thought, I was predicting that we could reach the point of equilibrium at 9000 and we went down to 6000 but that is fine now the only thing to do is to wait for the price to recover again.
There's are some points that are considered what affects the price of a btc. First is when a lot of investors sell their coin therefore the price of bitcoin will become low because of the number of seller. The higher the sellers the lower the price
Next is the social media or news cast about negative side of the bitcoin due to this, some people who are lack of knowledge about it is afraid to enter the cryptocurrency world because they are scared to lose and went for nothing.
FUD can without a doubt affect the market but things are not so simple at worst the FUD made the crash a bit bigger but nothing more it did not caused the crash that we are seeing, the crash was caused by fundamental reasons, people simply invested too much money in bitcoin too fast, some people realized this and began selling, this made the price to go down and then they panicked making the price to go down even faster.