Lemmy is not the Fediverse, and I happen to think it's pretty easy to figure out. But I've come from USENET > Forums > Reddit to get here. Someone who hasn't had that background sees a bunch of random links that are probably not of interest to them. Reddit has it's default "Popular" feed, and before that had a bunch of curated default subscriptions to get people started. Lemmy doesn't. There's Subscribed, Local and All.

"All" is a mess. It's super US-centric and all about their politics.
"Local" is of course dependant on the Instance. I live on ours, so I happen to like it. But, I can see how someone (particularly a non-Australian) wouldn't find it to their taste. Most instances will have little (or maybe one busy Community) in Local.
And finally you have "Subscribed". Which is empty by default. How is a new person who has never been on Reddit supposed to know what to do with that link? It literally has nothing.

Now, take that new person to something like Mastodon. Your default feed there is just the equivalent of All. And odds are someone's first taste of Mastodon is going to be all about US politics and people yelling about something. Again, not a great first impression.

"The Algorithm" as we loosely define it is supposed to fix this. It is supposed to bring you content you like, learn what you like and bring you more content that you like.