So the adoption of Bitcoin grows beyond this level, and the government succeeds in reaching out to the majority of the people by regulating a few crypto exchanges and passing bills that people (let's just assume they agree to) agree to. Those laws and regulations only bind the government and the individuals involved, not Bitcoin directly. Just as you have said, volatility is the nature of Bitcoin; it's part of what makes Bitcoin Bitcoin, so it can't change. We will always have a drastic change in price; that's one thing I know will never change with Bitcoin. No volatility means Bitcoin will be stable.
They cannot control the bitcoin network, but with regulations that will be imposed on centralized exchanges, and centralized exchanges are the places that hold the most bitcoins. Furthermore, all information about the market as well as the bitcoin price is displayed on centralized platforms, so I think they will still have some control over the volatility of bitcoin. Bitcoin is decentralized but used by everyone, and most of the participants in this market mainly depend on centralized platforms. The government doesn't control bitcoin, but they can control bitcoin users.