Actually, the free trial period with automatic billing at full price at the end of the period is a fairly common model that people in the US are used to (even if they don't like it); either it or the very similar discounted introductory period with automatic billing at full price at the end of the introductory period model is used for almost every periodic membership-based service that exists. So, I doubt very much that your statement about what most people are used to is accurate. (It may be what your experience genuinely was and the basis for your expectation despite the very clear explicit statement to the contrary that Amazon provides with free Prime trials, but I don't see any reason to believe, and have plenty of reason to doubt, that it is generally the case.)

And Amazon makes it unusually easy to cancel it for a full refund after the trial has expired and the full membership has been charged.