Blue Sky "fixed" that by only having one instance.

I suppose we could "fix" it in a similar way by inviting people to a specific instance instead of pointing them at join-lemmy.org.(Although that site has improved massively since the last time I saw it.)

Don't even mention instances or federation, just say "hey you should join me on ".

Once they are using it, that's the first hurdle, and they'll notice pretty quickly that there are other servers that all (mostly) talk to each other.