Because my Fediverse app is to the left of the Nostr one. That's about as much as I learned at school.
Different platforms for different audiences is one thing. I’m referring more to when people link their Nostr followers out to their content that very easily could have been hosted natively on Nostr. Especially with written articles/blogs. I assume it’s related to gaining subscribers or earning ad revenue on those other platforms. But Nostr handles written content well.