Because of the decentralized nature of the Lemmy system, you can't "ban politics from Lemmy."
Lemmy isn't one server, one site, one platform. It's a bunch of different platforms that follow the same protocol and talk to each other. Anyone and everyone can create their own Lemmy, and by default it will federate (talk to and share content with) other "Lemmies". For example, you are posting this to Lemmy.ml. That is one instance of the Lemmy software in action. I am commenting from sh.itjust.works, which is another instance of the Lemmy software in action. My instance is moderated differently than your instance, by different people.
It's a strong-suite of the open source, decentralized nature of the platform. We avoid censorship from bad faith parties, or from people who have no idea what running a social media platform should look like. Politics isn't going anywhere.