I think it helps to realise that yes, despite the rudeness it is normal now - because then you take it less personally!
I suppose it happens because OLD means you talk to / date men that have no other connection with you - so it's easy to do.
My friend and I refer to the ones that you hadn't met yet who disappear as "wandering off".
I think at that stage, it doesn't come from a really bad place and I have done it... You're talking to someone, you're not feeling it, you don't reply on day 1, mean to on day 2, by day 3 you think "well they've got the message, I can hardly mail after 3 days to say I'm not interested - that seems more rude and egotistical that just leaving it".
At that stage I have definitely ghosted - by default rather than callously thinking - fuck you, I'll leave you hanging.
After a date, I think it's damn rude.
However, again I've semi done it... If you're not interested and want to end it, you can either deliberately or unwittingly slow your communication whilst you work up to what to say.
I've always then said "sorry been quiet, tbh I've been thinking... thanks but no thanks" But I can see how avoiding the awkward conversation can becoming ghosting. Oh it's been a week now, I guess she knows...
I'm sure there are some callous shits! And it's always rude - but I think often it's laziness / gutless ness rather than meanness.
I have twice precipitated ending being dumped by texting "we text every day, it's been 4 - this isn't going anywhere is it?" Both times I guess would have been ghosting. And when prompted both were nice enough guys who ended things politely when forced to 
Nobody wants to start the bad news conversation.
Think my best ghosting was a guy who disappeared for 8 weeks genuinely because he was unexpectedly in a military bunker 