You don’t have to sign up for every instance you want to.

I can see that you’re currently signed in to your lemmy.ml instance, for example, and if you go there and search for a community in another instance, like gaming@beehaw.org, you’ll be able to view and interact with that community without ever leaving your instance.

So it is already linked in a way. Go ahead and try it out with some communities you’ve seen in other instances.

It’s called programmer humor for a reason: we’re just using established libraries instead of inventing a bicycle from scratch.