Why is there no auto-notification service for Amazon's Wishlist?
Having found one third-party "Wishlist Buddy" taken out of action by changes to Amazon's API, it is clear to me why it's unlikely that such an app will return. The wishlist function by itself encourages people to (a) return to the Amazon site and (b) direct them to the products they want to buy. If you are on their site, Amazon makes money: you're more likely to buy similar products, buy on impulse, share links or click through ads. If you're not on their site, Amazon would be losing money on informing you that individual products you have opted to track are being discounted.