Honestly, I feel like Mastodon is kinda never going to be like Twitter, even if its user count were to grow by two orders of magnitude. There are several reasons why, as the other replies point out, but the most important (IMO) is that Mastodon is just not a profit-driven platform. And if Mastodon is not a profit-driven platform, it is not designed to maximize user engagement. And if it is not designed to maximize user engagement, it is not designed to encourage toxic behavior.