This is because the only usage Bitcoin has left is a lottery ticket. Bitcoin used to actually have utility value (payment) but now with that gone, it is easy to manipulate the price because its value is built on people's perception only.
If Bitcoin was still being used to send money across borders, to buy things with super low transaction cost, send money without censorship-which by the way used to be why a lot of people saw value in it in the first place--it wouldn't be so easy to manipulate the value because any fool can see that there obviously is value in there.
Bitcoin losing utility has singlehandedly created the scam market we're seeing right now. People who want to make money choose the most efficient way to make money. And if they can see that they could make more money by building productive things on top of Bitcoin instead of building their own scam coin or scam scheme to manipulate the idiots who fall for it, they would probably rather work on those instead. But that's not the case, which is why we are where we are.