It's not easy to decrease the price of bitcoin if you have not big money. Bitcoin is the most stable coin. You can see its chart. It's the first coin therefore all coin base on it. Other coins have a lot of problems to be the leader.
It's the most stable because it's holding the dominant rate which is over 50%, that means slow movement of bitcoin
will bring bigger movement of altcoins as they are in one crypto market.
The price will go up and down but the recent trends are going down and that is because of the whales who love to manipulate the price.