Ad-supported or not has always been a choice for as long as Amazon has offered ad-supported kindles. I remember making this choice about 10 years ago, and I made this choice about a month ago when I bought my most recent Kindle.
If you bought it used or from a reseller, I don't know what to tell you, but Amazon gave you a choice if you bought it from them.
You can clearly see that Amazon offered the "with Special Offers" version alongside the versions without "Special Offers". The ad-supported version was discounted by $25 back then. Nowadays, it appears to be a $20 difference on the Paperwhite.
