You can also ask the opposite. What's the reason for the recent rise in crypto prices? Speculators...
The main reason is that some speculators got scared and others are taking profits so they sell.
Not all crypto prices have crashed Ethereum is close to all time high.
Only Bitcoin has crashed because of power outage in China. A lot of miners are based out of china causing the price to fall.
The prices fluctuate, sometimes wildly. They take a dip then rise up again. It's just a part of a cycle.