Some factors that cause this (and this is a good thing) is how original your work is,Hub construction and profitability rating as found in the details tab on the top of the Hub.
This is what I have surmised at least as you will see visitors to it as well which is the higher ups on Hub Pages checking it out. My guess is the score also can go up by them rating it up before it's released.
Is this all true,who knows but it sounds feasible to me and that's the conclusion I stick with. This is also a good thing as when you do choose to release it then you are higher up already and it looks like a Hub that people have visited thus spurring other people to follow suit more.