This is my thought as well. Lemmy isn't what everyone is looking for. It's a free open source software project for creating a decentralized federated network of content aggregators. For most people that sentence doesn't make any sense nor do they really care. They just want a site they can doom scroll for hours.

The people who choose to use Lemmy are people who care about open source projects, care about decentralization of online platforms, or both. These types of people by their very nature support groups of people coming together collectively to do something big.

A collection of people working together towards a common goal without a strict hierarchy. You could say these people are community focused. Maybe we could call that communityism or something. Where people make rules as a group, or a union you could say. So yeah, no idea where the left lean is coming from.