A lot of my WCH cards are irretrievably unbalanced and, lets face it, rubbish.
When I find the odd one that I like, I have to make art for it before I submit it. Not an official requirement, but my own. And that art has to be good, it can't be "yeah that'll do" art. And art can take a long time to get just right.
For example, just yesterday I was arting my Psychic Pillar. I spent so long working on the base pattern, then when I extruded it took so long to connect it to another bit, and then I hollowed out the top and that took hours because apparently SketchUp doesn't like me drawing circles.
Eventually it was perfect. Then I rendered it. And it looked like something a five year old would draw.
Takes a while to do art, and in terms of time, that's my limiting factor for WCH->LCC.