There's a reason for this. Amazon started before the widespread availability of free email services and it was quite common for a family to share a single email

There's a reason for this. Amazon started before the widespread availability of free email services and it was quite common for a family to share a single email address from their ISP. They built this feature in to allow for this case. I knew an engineer who interned at Amazon who's responsibility was to maintain this legacy system as there were still quite a number of active accounts that shared the same email address.