Im going to rewrite my comment since I wrote the last one while in line for anime expo lmao, and left a lot out:
The "it factor", i think, can be rephrased as "luck". IMO, there ARE some comics that get """""""lucky"""""" and reach popularity that may seem undeserved. But I think, that really isnt luck, there is a formula for how an audience reacts: Maybe vampires are really huge and this novel happened to be about vampires and blew up? I wouldnt call that "luck", but rather being at the right place at the right time.
For most people though, we really shouldnt even be betting on luck. That is completely out of our control. What we can control is the quality of our own work.
More often than not, popularity trends with quality. Good art, good story, good characters, will correlate with success. There are other factors you can take advantage off too like maybe popular art styles and genres but at the end of the day it is not a single art style or genre that sells a story, it is the whole package. The genre, art, story, etc are all letter grades that balance to a nice GPA. You are aiming for the highest GPA possible.
The biggest issue I see is people blaming outside factors for their lack of popularity. If you have good work, they will come, so to say. Sometimes this means taking a step back and realizing you have a LOT to improve, and improving it. The common factor I see in most successful comic artists is the tendency to look inwards and see how they can change their work to meet a market or how they can improve their storytelling, rather than blaming the audience for being ungrateful bastards who cant appreciate real art.
So anyway, does an "It" factor exist? Id say no, the it factor is just a good GPA on a comic. Maybe the comic has a D in art and youre shocked its popular, but it has an A+ in market trends and an A+ in story youre overlooking.
And maybe you can do everything right and still fail, but I find this possibility so unlikely that you really shouldnt be scared of it. If you think about getting hit by a car every time you go outside, youll never be able to get anywhere.
But thats just my two cents...