A default instance is not ideal, but adding a barrier to joining is counterproductive. If someone has an interest in a specific area, they should be directed to join programming.dev or slrpnk.net etc. If they want a general purpose instance, then they should just be assigned a default.

Personally, I started the signup multiple times because there are hundreds of servers and if you haven’t already used the platform it’s impossible to know what you need.

Anyway, more than promoting Lemmy as a platform, we should be promoting Lemmy content. Mostly it is publicly visible without an account, and if someone sees Lemmy links 5-10 times, they may start wondering what they are missing out on.