My theory:
People here hate Soyjak because it breaks their bubble of ignorance and shows them how the world at large sees them. Standing out sharply among popular content like esoteric fetish material and the obsessed commenters who consume porn here en masse, they see something that does not affirm or encourage their distorted worldview, but instead challenges it.
They see the out-of-luck, product-obsessed, immature man as a twisted reflection of themselves. The jarring, immediate contrast of these memes among the usual light humor and obscene fanart posted to this site is enough to cause a violent reaction. Even a relatively small number of uploads per day (compared to the truly popular galleries) is enough to disrupt their sense of belonging, enough to pull them out of their extended period of blissful ignorance. How else could one gallery attract such vitriol and hatred? Why else would people go as far as deactivate their accounts and quit the site because of one gallery?
The beauty of Feels Guy/Wojak is the introspection it provokes in observers, and the solemn recognition of depression and severe loneliness thinly masked by irreverent humor. When you see a Feels Guy meme, you may recognise the pain as your own. You may feel bonded in sadness to Feels Guy and maybe even whoever made the meme you're looking at.
But not with Soyjak. With Soyjak, people may still feel personally connected to the meme. But Soyjak memes are not made to be relatable. They are made to mock those they depict. When they see themselves in Soyjak, they feel only shame and anger at being the object of such widespread ridicule, and at the portrayal of their internet exploits as pathetic wastes of time.
It's not that people hate Soyjak itself; they hate the cold, hard dose of reality it injects them with. Their elaborately-constructed suspension of shame and doubt, all destroyed by one MS Paint drawing. Like a twisted mirror image, the sense of fellowship they once felt with Feels Guy has been brutally corrupted by Soyjak.
"Same things make us laugh make us cry" – Big Smoke