Waves DEX is a decentralized trading platform. In decentralized exchanges, you do not require a third party to store your funds, instead, you are always directly in control of your coins and you conduct transactions directly with whoever wants to buy or sell your coins.
However it cannot be compared between Bitcoin and US Dollar, because Bitcoin is a crypto currency while USD is flat / local money. So the USD is recognized by the whole world and can be exchanged anywhere, while Bitcoin is not, so this is a wrong comparison.
The volatility of bitcoin as well as the crypto currency market depends on the investors who invests and who sells the coins. The more invest in bitcoin the higher the value it would reach and the more who sell or dump the coins it means the price value would go down even on its peak that causes people to panic. We can relate it in the law of supply and demand.