Yes, it is the editing fees. Nth-tier universities in many countries are pushing faculty members to publish more. This is all done with the best intentions -- we all want faculty at the cutting edge of research. So many of these universities offer financial incentives of various sorts to faculty who publish more. For instance, they may tie pay hikes or promotions to the number of publications. There's often grant money available for research (and publication) to support these activities.
This has led to the inevitable unintended consequences. Most of these faculty members do not have the resources or the ability to publish in "real" journals, nor do they even understand what a good journal is. So they publish in whatever venue that accepts their paper. If it requires them to pay, then so be it. And thanks to the beauty of capitalism, a bunch of predator journals have emerged to lighten the purses of these poor folks.
This has led to the inevitable unintended consequences. Most of these faculty members do not have the resources or the ability to publish in "real" journals, nor do they even understand what a good journal is. So they publish in whatever venue that accepts their paper. If it requires them to pay, then so be it. And thanks to the beauty of capitalism, a bunch of predator journals have emerged to lighten the purses of these poor folks.