What those people really need is to have their opinions challenged by outsiders. That used to happen more on the early internet.

Keep in mind that they didn't leave Reddit because they wanted to leave. They left and made Voat because they were banned. Now they don't have to interact with people that have dissenting opinions, and they can ban you if you dissent.

Reddit is relieved because their users are no longer exposed to this toxicity. Unfortunately, now those users are no longer exposed to anything but toxicity.