Why would you follow the same accounts on multiple platforms?
Or do you mean one person who has accounts on multiple platforms?

Yes, people do. Thankfully we as a community aren't bound to corporate shareholders, so it doesn't matter how many people choose to use it, we don't have a need to increase users. While we don't have a fiduciary duty to be kind for similar reasons, I think it is generally a good idea to do so. In my experience when I have used words/phrase like "everybody" "nobody" or "people don't" some have told me they found it off-putting or belittling when they are in the minority so I try to avoid it but I still find it hard sometimes as that is not the way I was taught to speak in government indoctrination camp so there is a lot of de-schooling I need to do.

I can from a number of other Fediverse platforms. I may not be able to follow you on Lemmy like I can follow a community, but I can still find your account to see your posts and comments, and that limitation doesn't really impact me having to have per-instance accounts versus having a fediverse-wide account. I have probably a dozen fediverse accounts across multiple platforms. I want to have my fediverse identity able to access all fediverse platforms and that other people using that platform can find me as.

I sure do like this picture:

So like a single ActivityPub instance that hosts all the data, but users can have a Pixelfed app, Lemmy app, etc. all connect to that one server and use it to give the experience they specifically provide.

That's a cool idea. I can see how that would work.

And that's great! Everyone gets what they want. But suggesting Lemmy, Pixelfed, and Peertube, etc. should all try to do it the way Friendica does, is a bad idea.

If I have a mutual who is on multiple platforms, and I also have accounts on those same multiple platforms, we would generally be following each other mutually on those same platforms.

But your saying Peertube should have all the forum functionality of Lemmy, and the endless short video scroll of Loops.

rgluilis suggested a generic server idea, where the media and experience differentiating is done at the client app level. That could work well. But that's an entirely different cincpet and structure.

The writing in this article it absolutely terrible. It needs some serious clean-up before the message isn't impaired by the medium.

You jest, but I'm pretty sure someone out there made a cli interface for AP.