There are many factors to think about as possible reasons that give rise to proliferative number of publications in predatory journals. Arguably, article publication charges has been pointed as the possible stem cause. Do you believe in this?
Sometimes, people may be looking for cheaper APC without considering the quality, in this route they fall in the pit. But, even there are some journals without charges and do well, so no point in falling to the pit of predatory journals.
No. You cannot generalize. Publishing involves cost, and there are several legitimate ways to meet publication charges of esteemed journals. People go for predatory journals to circumvent the process of pee reviewing and easy and fast publishing. Do't forget that predatory publishing itself is fraud and it thrives based on the levy demanded from by contributors!
The answer is to not submitting to predatory journals, and instead submit to ordinary ones - the usual ones from your past - and simply do not pay the open access (OA) fee if you don't have money for it. My institute is not always very generous with help to cover the OA charge, but one can still publish the paper!
You question is very important. Sometimes the APC is quite outrageous even for some quality journals with high impact factor e.g MDPI journals (sustainability, agriculture etc). Also, there are journals that are of high quality and do not request for any publication charges e.g Elsevier journals. The issue with such journals is their submission to publication takes up to 8-12 months with lots of stringent guidelines.
I agree that issue of APC for most quality journals give the predatory journals to thrive. With journal charging up to $600 for a paper publication and a journal charges as low as $20. A author that doesn't have such financial capacity to pay as high as $600 may consider the lower APC. For me, I search for journals with quality publications ad preferably with zero APC.
I agree with Prof. Michael Patriksson. You may still get your manuscript in quality journals by not paying for open access(OA) and still get your manuscript published.
Yes, it is the reason for proliferation of predatory journals. But why pay to get a paper published? I have never paid to publish. I only paid for reprints.
In my university, online journals do not count much for appraisals so why waste so much research labour for what will not count.
It could be part of the reasons for proliferation of predatory journals but I believe the major reason is to be rich by all means without considering the implications to the society.
I will rather patiently have a good peer review than hurry to publish unreadable, grammatically wrong and misspelt publications put up in some open access, online journals; surely not after a laborious research. The hurry and payment even if the amount is small are not worth the poor finishing. Peer-review is very useful.
The predatory journals may proliferate but, like the current ''fake news" from journalists, may not be read by serious colleagues, researchers who would make much useful input were the paper properly reviewed. Rather corroborate with few peers than a world of fraudsters whose intent is always evil.