The primary goal of stablecoins is to reduce or stop irregular price volatility associated with Cryptocurrencies. Exchanges do this by pegging it to a USD value. They do this to keep the price closer to usd as much as possible. Stablecoins are important for traders and crypto users to preserve their usd holdings value
Stablecoins don't reduce the volatility of crypto at all. It's just a token that should replicate the functions of regular fiat currencies, but add certain advantages for traders. Quick movements between exchanges 24/7 is the main advantage, and the very fact that stablecoins are more likely to stay within the crypto ecosystem during bear markets, while fiat currencies are more likely to be withdrawn back to people's bank accounts.
Stablecoins is money in the market waiting to enter, and you can be sure that it will eventually.