It's simply this. After all these years I have yet to become comfortable with doing the line-art in preperation of coloring..
I've looked up many tutorials and have tried different techniques, but for some reason I still haven't become comfortable with it.
Most of my energy when trying to color goes into trying to do the line-art. I also start to lack patience halfway through doing so, or coloring.
I know I have the skills to do a far better coloring job than I have done recently, but with my lack of time to actually sit down and concentrate on it like I want to I am far more likely to just rush everything.
I have been working on a new drawing though. I already re-lined the artwork in Open Canvas so I'm kind of going to have to color it in that now, but i'm going to try not to rush this one and see how well I can get it to come out.