If you mean cryptocurrencies, they do not. Cryptocurrencies are free floating on the market depending on market sentiments and also other factors. Stablecoins on the other hand are tethered to fiat currencies such as the US dollar. However, because bitcoin is a cryptocurrency with a large market cap, movements in bitcoin price may cause sentiments that can move the price of other coins. Because of that, it may seem that they are tied to the price of bitcoin.