The scuttlebutt is that it's a inside joke by the far-left dev of lemmy to stand for marxist-leninist, but it's just as likely, if not more, that it was chosen because it's free.
Keep in mind that most (all?) two-letter TLDs are associated with a country. This includes stuff like .io
, .tv
, and .me
I'm kind of curious about how you think the internet works.