Given the way this is tagged up with the @ and # throughout the comments I’m venturing it originated on Mastodon, yet here I am commenting on it from a Lemmy instance. Some of the inconsistencies of the federation between different platforms are going to come down to them each having different focuses, and that’s plenty good. Trying to jam every functionality into a single platform is likely to result in it doing none of them well.
For my part having the ability to see one from another is a neat bonus, but not the main driver of use. The format and style of interactions leads me more towards things like Lemmy/K-Bin where some find Mastodon, Pixelfed, or any of the Friendica/Hubzilla style page base ones to be their thing. It’s even possible people like more than one. I host both a Mastodon and Lemmy instance, and have toyed with others but didn’t find them compelling enough to maintain.
So no, the notion of talking across platforms isn’t so much the huge point of the fedi in my mind, but toss that in with the ability to do what you want to do similar to any of the big social platforms (they all pretty much have some kind of fedi counterpart now) without selling your soul to the corporate overlords is pretty fn awesome