Keep in mind that not everyone can buy ASIC miners, so for some GPU is easier choice. Also there are some features that GPU have which ASIC miners don't.
I already expressed the same things already. Asics = unfair competition cause not everybody can buy it.
I think you are underestimating the number of manufacturers and there volume of productions, Sapphire can produce around 100k pcs a week (first hand info, they don't even negotiate with traders for less then 20k pcs) not to mention that in that total hashrate there are tone of rx550/560 cards from 2014/15 so the number of gpus could be higher, stretch that on 3 year of manufacturing you get like approximately 400k GPU's a month this is easily achieved with all the vendors combined
All are related to how many chips memory makers can provide to them, how many chips amd can provide them, from december 2017 to now is impossible to have such hashrate with gpus. My point is to have that kind hashrate in 2 months took eth network 3 years. So is impossible eth network to double in 2 months with imaginary gpus, it took 3 years for that hashrate to happen and after they started putting asics on december 2017, it doubled in 2 months. So my point is imagine april 2015 to december 2017 let's say 10 million gpus and that is 3 years putting gpus in the network, now think about from december 2017 to january 2018, people add 10 more million gpus, is impossible cause manufactures cant manufacture or produce 10 million gpu that took them 3 years in 2 months.
So whoever says that network increase is gpu and not asics must go to a doctor and have the insanity test.