@bgbuk
One reason is that unlimited PU’s are not supposed to exist (well, they do on some hacked versions of some games), so that PU leaderboards would be highly correlated with the amount of money people would want to spend for it. Moreover, there are some platforms (PC, for example) where PU’s are not present at all.
Assuming that this is not an issue (i.e. everybody plays with hacked version with unlimited PU’s), my belief is that if you are a good flinger without PU’s, you’ll also be an equally good flinger with PU’s, so that adding this extra leaderboard will not change anything to the picture.
The only added value I see for PU’s is that for several levels I have investigated, the best strat might be completely different with or without PU’s, so that they are in some sense very different levels. But since almost no one has played all levels of all games in the normal way, I doubt that doubling (roughly) the number of levels by including PU leaderboards will be of interest for most people.