Surprised to see this thread bumped up. Almost forgot I created it last year.
It's funny how it was almost a year later for mining profitability to drastically reduce to the point where we see loads amounts of GPUs all over Craiglists and eBay.
I also wonder too if we will ever get a mining boom again. Even if the ETH and BTC prices finally start going back up, the difficulties are just crazy high to go back to the $5/day/RX 470 profit levels.
In bearish market they are less coins profitable to mine so diff is higher, when prices are going up more coins is profitable and diff is going down a bit or stay the same level. When they are extreamly high profits per card many ppl start buying GPUs and diff start rising again

So it's normal market process imo.