It was made by Marxists, along Marxist principles. FOSS in general is often home for those rejecting the decaying Capitalist hellscape. It takes a particularly ideological sort to choose Lemmy over the much more established Reddit, Lemmy doesn’t exist in a vaccum.
There are definitely non-leftist/right-wing, liberal instances like Lemmy.world and sh.itjust.works, but generally Social Issues like LGBT rights are universally supported.