The cryptoworld is full of coins that are highly volatile, you can easily buy and sell cryptocurrencies whenever you want to, so I think, that is one of the main reasons why cryptocurrencies are just so volatile. Another is those whales who are trying to control the price in the market, and that makes the value of the coins so volatile as well.
But among all, bitcoin has its own place. No one can reach its level. It has become the most used coin in cryptocurrency world. Some other altcoins like eth and LTC made good history too.