Well, /tells and discord are kinda similar. Though some might just have their settings at "super private" or "no notifications". *shrug* I dunno.
I'm not on FB, and I generally don't put my game email out there (and I rarely check it anymore). I was never one for really getting overly involved in the social platforms (I didn't do CoH Faces, no Twitter, no Instagram, etc.,.)
As for the forums, I know some folks who avoid them, some who check them periodically, and some who check them regularly. It may be a case of folks just getting the messages late and then figuring it didn't matter anymore.
Or, maybe ghosting is just the newest way for people to indicate they are not interested (which I would agree is kinda rude).