The intent of IJS was that PE, CH and IN would explicitly reward good presentation based on defined criteria and not the whims of the judges' tastes. In reality, there seem to be two problems (IMO).
First, the PCs are not being used correctly (as intended) by the judges. As a result good presentation often doesn't get rewarded if the elements are weak, and mediocre/poor presentation gets rewarded if the elements are strong (Plushenko OGM). This is the fault of the judges and not the design of IJS.
But there is also a second problem with the design of IJS. Say mediocre program from a skater of decent technical skills is going to get the usual 5-6 points in PCs. To move up by 2 points in each of PE, CH and IN requires a huge investment of time and effort. For all that work, a man's PCS score will go up 12 points. However, if for the same amount of work (or less) you can get a 4T and execute it twice in the FS, you get 18 points. So I think many skater do a quick cost-benefit and say, I can get more points learning more difficult tricks than investing the time in improving presentation. And if I improve in technical skills, it will pull up my PC scores anyway.
On the other side of the equation however, if a skater has reached their full potential in elements, then the only place left to earn more points is to improve the PCs. But most skaters it seems never lose hope that they will eventually get the next big jump, and so they flog the elements at the expense of the PCs.
Great post. Thank you for your insights.
But I think that some people are simply more talented and find it easier to improve presentation than jumps despite that it is not necessarily cost-effective in terms of earning points.