Think about things from the point of view of someone who has never used Reddit or the fediverse, but you've heard about them both from recent news articles and want to see what they are about.
Reddit:- You Google Reddit and your first result is Reddit.com. You click the link and are presented with the front page. You from scroll from a few hours and end up signing up and staying.
Lemmy:- You Google Lemmy and your first result is a wiki article for Lemmy Kilmister... Your second result might be join-lemmy.org, which you're smart enough to realise it's probably more likely what the news is about.
You click join-lemmy.org and are presented with a page of information about the fediverse, links to set up a server and pictures of code...
There is very little chance you're going to investigate further.
If we want the fediverse to replace Reddit then either
A) Lemmy needs to improve its initial impression and Search engine optimization
B) We should be promoting a different platform with a better initial first impression.
I'd recommend kbin personally as it gives the same sort of experience as Reddit from the initial interaction.
I think part of it is that leftists (myself included) don't like being lumped in with tankies. I didn't downvote though.
The lead devs of lemmy are tankies, basically meaning authoritarian communists of the genocide-apologist variety. They also run the lemmy.ml and lemmygrad.ml instances.
This is also why I signed up on kbin instead of on lemmy. The other lemmy instances are fine, but I don't want to contribute to the influence of the lemmy devs any more than necessary. Hopefully they try to pull something stupid and get forked off the project.
Why would anyone downvote for that reason though? That reason is why I upvoted. I'm firmly left-wing but absolutely not far enough that I can support their BS views.
Most likely because American politics frequently pound the talking point of "far left politics" when talking about the political opposition (moderate left at best from an overseas PoV), to the point where American liberals have been conditioned to assume that they are being spoken down to when this type of language is in play. American leftists are also very anti-authoritarian on average and do not appreciate being lumped into the same category as tankies by simple virtue of people only discussing left versus right.