Because there’s no meaningful way to answer that here. It’s like asking what’s the difference between trawler fishing and open cast mining.

I'm sorry you're getting downvoted, but I think this question is legitimate because the book is peddling Kafka as if it's the only way to do event sourcing. Event sourcing is what you should compare with REST APIs, Kafka is one way of doing it, but you can do the same with any database, as long as you have a way to write things in and read things out and organize them, you can achieve event sourcing.

With REST APIs (first few pages of the book), services talk directly with each other, with event sourcing (the rest of the book) services talk with an event store (Kafka in the book) as the intermediary.

You're getting downvoted because your question makes no sense. They are not related at all, which means you must not have read the link.