I have no idea but I can guess. It's actually quite natural for writers to want to write omniscient (even if they don't know what it is).
Writers know everything. We live in these characters' heads all day long. We know where the story is going. We know how it's going to end. We know what these characters don't know (at that point of the story).
So it's natural for the writer to want to tell everything, and what everyone is thinking. I call it the "telleverythingitis" and it's very common among writers, new or seasoned. Also, being the author, we tend to have a god-complex -- we can make the characters suffer, etc. So why can't we know what all the characters are thinking, or that a bridge is going to land on them?
On top of it, any kind of limited view point (1st person, 3rd limited, even 2nd) seems tough and contradictory to the way authors think. We know everything, and yet you're telling us that we can't tell people we know everything? That we're only limited to what ONE character knows? An undisciplined writer would have twitchy fingers -- feeling like, Gosh, I'm in Mary's head now, but I just WANT TO TELL you all what Jack and his dog are thinking too. How else are going to know if I don't tell you?
It's a combination of not knowing how to reveal information/create suspense with a limited view point, and the desire to tell everything in our writer's head.
Of course, people could be drawn to it for the right reasons. Omni has that sense of epicness, that "once upon a time" timelessness, and also the all-knowing nature of storytelling can be magical, because it's not like real life. That's why omniscient, often, is suitable for fantasy or science-fiction, or any type of epic adventures. It's not very suitable, however, for intimate personal dramas.
Someone said omniscient creates intimacy. I'm not sure why. Omniscient is the most distant narrative. Someone is sitting on a cloud telling us stories about other people. To me, there's nothing more intimate and personal than 1st person. And just because 3rd person doesn't have a VISIBLE narrator, it doesn't mean no one is telling a story, but 3rd person limited is somewhere between 1st and omni, and you can create almost the same intimacy as 1st person, with a thin layer of detachment, with 3rd limited close.