Sure:
Amazon started its history with a deep affiliate system whereby "anyone" (capable of creating an affiliate account) could create affiliate marked links to get a small profit share on items sold, plus marketing reports and other information (which only grew more detailed over time). Because of that, affiliate links are everywhere on the web. Advertising companies themselves also use them both to get an extra cut on the advertised item and also to get those juicy marketing reports for ad spam.
Originally affiliate marks in URLs were easy to spot, they were just query parameters (after the ?) and removing all query parameters removed affiliate info from Amazon links. (There are still ancient ones out there like that.) After a while, and I don't know when the transition date was, these started to get embeded sometimes "steganographically" in other parts of the URL.
At one point, as a blogger with bloated ideas of my own influence I set up an affiliate account for myself. For a few years after that, I liked to use Amazon in "Affiliate mode" where it had an extra toolbar at the top that would let me at least take any link I was looking at and replace any affiliate marks with my own. I could use that to stop sending marketing info to links that I had followed (and sometimes make a couple pennies back on purchases, like one of the world's dumbest credit card rewards systems).
The way Amazon Smile operated is that it basically earmarked the money that would have gone to an affiliate for the charity of your choice. (I wouldn't be surprised if Smile had just been implemented as a pseudo-affiliate, which also adds to other conspiracy thinking that Smile might not have been that hard to maintain from an implementation standpoint.) Because the charity was set in your user preferences there's no use for affiliate marks in URLs, so none of the smile.amazon.com URLs have affiliate marks at all because they don't need them.
So the easiest way to take any www.amazon.com URL you could find in the wild and make sure it didn't have any affiliate marks and wouldn't send data or cash back to an affiliate was to simply replace www with smile and let Amazon's own backend refresh the URL without affiliate marks. This was useful for cleaning your own browsing histories of marketing data and also for making sure that if you were forwarding links on to friends and loved ones they also weren't accidentally sending tracking data back to some affiliate with no real need to know.