I actually don't think I'm missing the point and posts like these prove it to me. Why so much animosity towards them?
Because if it was just ignorance, either "genuine" or "purposeful," and they've taken this opportunity to listen to someone (TB and his biscuitbitches), learn from the experience, try to exact some meaningful change and something positive out of it, and ultimately pulled out of the relationship, then why not celebrate what to me seems like a very positive outcome? Big company actually listens to its fans, and as popular as TB is, he's far from someone on the level of PewDiePie, tries to do some positive, and follows through.
Both you and the article posted seem so skeptical of Gearbox's true intentions and even go as far as accusing them of lying about not knowing about G2A. I mean, if Gearbox is a big company busy making games, it's not beyond the realm of possibility that they aren't going around keeping track of every digital video game marketplace, watching every youtube gamer video, and reading every random blog post on Kotaku so that they get approached a company, do a cursory search on them, see that they seem legit (and honestly, if you just do casual research on G2A they come across as very legit) and decide to do business with them.
Like I said, all this reeks of underlying animosity towards Gearbox for whatever reasons (oh, they're a big company or whatever) and not really fair or genuine.