What happened to these people was not a 'demon specific' occurance.
It was a test organised by bored and interested minds into the capabilities of themselves and mankind.. Portals and such are merely illusion, Demons with name are generally the repeated test sequences to define localised results.
Others are taken to this early in life by assorted criminal acts being made by themselves or by those minds which wish to test in their boredom.
Forces with name are sometimes eternal.. Though it is rarely spoken of unless further testing to procure result is required, when results are ascertained, return to normalcy occurs, the occult takes advantage of this fact and sometimes requests it too often.
Unfortunately, even in the event of entire world agreement, testing will continue til space travel is normal, for temporal psychological study cannot be proven to be black and white as yet.