I don’t have plans to visit other instances, manage multiple credentials. Either I get to see it all from one place. Or these other places will functionally but exist for me.

You don't have to manage multiple credentials. You can visit and subscribe to /c/knitting on another instance as long as your instance is not blocking it, or blocked by it.

If I subscribe to /c/knitting I mean I want every /c/knitting on every single instance in existence.

Would you? The point of having multiple instances is that /c/knitting@gaming.lemmy will be mostly about knits inspired by gaming, /c/knitting@memes.lemmy will be mostly about knits inspired by memes and so on. You may not want all of them. This is a bit of a stretched argument, but I want to showcase an example where fragmenting communities on a per server basis can be useful.

I know that for generic communities or hobbies it can be annoying, but it isn't that hard to find the largest /c/knitting and subscribe to that, no matter the instance. Reddit's centralized approach is more convenient, but we've seen the price we have to pay for that convenience.