Bitcoin now costs a lot and so many can not afford it. Reducing the price of it helps to invest in it for those who believe in its success. Large investors also tend to buy it at a good price and so they can specifically manipulate the price to their advantage.
For now bitcoin experiencing huge dump of demand in the market due to some investors pulling out their investment in some exchange like in binance there is a huge bitcoin withdrawal happend this year that is why it has a huge effect on the demand and price of bitcoin and altcoin was affected.