Because the cryptocurrencies are ruled by the Demand and Supply law , higher demand tends to increase in price and decreases when supply is not enough. The market of crypto is like a glass full of water that tends to overflow when added (mined) , now every movement in cryptocurrency can affects to its value.
Every market is ruled by demand and supply,be it gold silver or any commodity market ,the demand and supply determines the price of a product,do you think that mining new coins will affect the market,after all bitcoin is limited and there is no bitcoin for everyone in this world to own,the number of users are not that big and so is the reason we are seeing these sort of volatility.
I couldn't agree more, there is an artificial demand for bitcoin so to speak that has been created by its limited supply and the minimal number of people holding and using them compared to the greater world population. These factors makes it volatile whenever more people(mostly newbies) seek bitcoin and invest in them and whenever there's a loss of interest and many holders sell.