I've never heard anyone (at least not anyone who wasn't already using GIMP) complain about the concept of paying for it, it's always been the way Adobe tries to squeeze extra money out of you. First it was bundles where you'd have to buy software you didn't need to get what you do. Then it was a subscription. Also, each CS version seemed to add very little for the price.
Their sales went crazy because everyone was relentlessly pirating their software.