Amazon tries to justify this quite radical increase with the fact that in the last decade it managed to increase free shipping to millions of items across all 40 product categories. The solution for Amazon is to persuade you to choose the Amazon Prime and upgrade your membership for $79 a year.
For this fee Amazon offers free 2 day shipping on millions of items regardless of the price, Unlimited instant streaming of 41,000 movies and TV episodes and over 350,000 Kindle titles to borrow for free.
You can see if for yourself here.