Lemmy was built by Communists, along Communist principles. Lemmy.ml is the "main" instance, owned and maintained by the Communist developers. The .ml is a reference to Marxism-Leninism.
.ml also focuses on FOSS and Privacy, but is very much a Communist instance, though most Communists go to Hexbear or Lemmygrad.
You're on a platform built by Communists, just because Lemmy.world blocks most of the explicitly Leftist instances doesn't mean there aren't a lot of Communists on Lemmy.