Users are now purchasing refurbished smartphones more than ever due in part to slowing innovation and marginal design changes on the latest models. The hardest hit are mid-range smartphones as used high-end models from Apple or Samsung can be had for about the same price. Why purchase a brand new flagship when last year's model is very nearly the same for hundreds less?
https://www.notebookcheck.net/Refurbished-smartphones-are-selling-almost-five-times-faster-than-the-year-before.289240.0.html
For the year of 2017, it was the flood of bezel-less phones and in my opinion a peak in craftsmanship from key players. It's difficult to argue purchasing new releases in 2018 so far when you can purchase 2017 refurb/used phones for more than 50% of the price difference of new 2018 phones, (I actually just picked up a refurb S8+ for $360 last week).
I totally agree with you, but we should also add that new releases are sometimes worth it, especially in the mid-range sector, where software support has improved a lot in the last year. After all, why not get a good device priced around US$200-250 that will receive major Android updates for around two years?
There is also the problem with Samsung's custom interface (Huawei EMUI as well, Asus ZEN UI, and so on) that lead to slower arrival of major Android releases, while Android One phones get it in a jiffy.