I think a large portion of that hashrate is all the GPUs switching of ZEC since it's completely an Asic coin now. A few hundred thousand GPUs is less then the hashrate that was on ZEC and there's zero point in GPU mining anything on the Equihash algorithm now.
If all the ZEC mining GPU move to ETH, it will only increase the ETH has rate about 15%. I think that is the ETH ASIC.
It is likely pressure from both fronts, as Equihash miners are now switching over to ASICs freeing up their GPUs to mine other coins, which right now mainly means moving to ETH. Also, the Antminer E3 is due to ship in late July, but I bet some are already starting to trickle out to large farms or other well-connected miners ahead of time, thus also driving up the hashrate.
Combined with the current downtrend in all coin prices this is creating the perfect storm of destroying any remaining profitability, as hash-rates and thus difficulty skyrockets while at the same time the coin prices plummet. Happy times are indeed here again, enjoy!