1) Replies are in "replies" or "conversations" list. Boosted notes are in the "OP" list and reach a wider audience because many npubs only enter threads from the top level.

2) Boosted notes are their own event and can independently appear on a trendlist, which increases their visibility to an audience that isn't only the npub's own followers.

3) Not everyone is following you (I know, hard to believe), so his own followers might not see your OP note and completely miss the conversation.

4) You're right. I know nothing about Nostr. Clearly. Glad you could educate me.

5) Because you're not the only one who asks these passive aggressive questions.