I would say that the main issue is the difficulty for a company to create a "1-size-fits-all" template that caters to different gaming groups. You have some parties who are extremely optimized, and others with less optimized PCs. Where do you settle for a middle ground? I have heard reports of lv14 parties taking down the tarrasque, others still having problems with it at lv20.
So the disparity is even more apparent compared to lower levels.
So the disparity is even more apparent compared to lower levels.