Amazon's hallmark in the past has been investing big into businesses without immediate profits. Amazon gets massive revenue but has nowhere near the margins of an Apple, or Google. As you know, a net loss and revenue are not apples to apples. For full year 2018, Amazon had net income of $10B on $232B of revenue.

All of which is to say that a $5B loss is a very material number. They obviously thought it would be a big profit driver in the future, which it has not turned out to be yet.