I had the same issue until I discovered there were plugins for Chrome[1] and Firefox[2] that will automatically redirect you to smile.amazon.com anytime you are on amazon.com. I have seen issues with the Firefox one when you aren't actually logged in to Amazon at the time, but the Chrome one works great.
Thank you for pointing this out. I wasn't aware of that extension. I've only generated $14.12 in the multiple years I've used smile (inconsistently). It'll be interesting to see how much that changes in the next year.
[1] https://chrome.google.com/webstore/detail/smile-always/jgpmh...
[2] https://addons.mozilla.org/en-US/firefox/addon/amazon-smile/