Isaac Asimov averaged an original book about every 6 weeks over the time between his first book was published and his death. He also averaged editing a new anthology or collection of prior work (his or others) every 15 weeks. He also averaged a non-book story every 6 week. And an essay every 9 days on average. Oh and also an average of about 6 letters or postcards per day(!).

For his books (authored + edited) that comes to an average rate about two orders of magnitude under Amazon's limit. Even if Asimov had stopped writing non-book stories, essays, letters, and postcards to devote more time to books, he probably would still be an order of magnitude away from hitting Amazon's limit.

I assume Amazon wanted to set their limit high enough that no legitimate human authors would hit it, but they were way more conservative than they needed to be.