Too many terrorist simps, too much mod abuse, too much disinformation, too many Tankies, discovery of communities is hard with how federation works and kinda requires third party apps.

Finding instances for sure. Just learned in this thread that sorting by 'all' doesn't show me every instance

The fact that many on the internet haven’t gotten past the largest hurdle, creating a Lemmy account.

We’re currently at 462k created accounts.

Many instances have domain names that look invalid and/or like scam sites to non-techies. Dot world? Dot social? Dot [obscure country TLD]? There's also no guarantees that the domain will indicate that it's a Lemmy site. Both of these become problematic with sharing, as the default (? been a while since I've used the web interface) share function links to the poster's instance and not the community instance. A year and a half ago, the shared links section in my messenger was mostly a Reddit flood. Today, it looks like someone spilled alphabet soup.

The default web interface is very poorly designed and looks uninviting. Sure, there are great alternative interfaces but people will be turned off before they could check them out. Also, it's usually the first thing you see when someone's sharing a link.

There not being an official app is also something that will confuse non-tech users.

That it's not well known.