It goes against our sensibilities of fairness. We expect that all consumers should pay the same price for a the same item, regardless of age, race, gender, or browsing history.
And what about student discounts? Is it unfair that students get better deals on Photoshop and Microsoft Office?
I guess my main issue here is the clickbaity title, since I don't think Amazon is making us suckers. The consumer ultimately has the upper hand since they can just choose not to purchase the product, or use a price search engine to find a better deal (which is akin to using a coupon - people that are price-sensitive are more willing to put in effort to save money).