Obviously the pass rate is trending down. But if u look at the populations, there were actually more and more people taking these exams. And the number of passes pretty much has an up trend. So it's really hard to argue whether the rate drops because of the exams were getting harder or simply too many people were taking or trying the exams. On the bright side, CFA institute is absolutely expanding their business though.
One interesting thing is since 2003 when the L1 exam was first offered twice per year, the pass rate of Dec exam is systematically lower than the one of June exam, with exceptions in 2004, the only time Dec's rate occurred greater than June's , and 2008, the only time those two were equal. Sure one can argue that 1-2 percentage points difference in pass rates could be very well within error range and can't mean anything substantial. But thing is with that pattern repeating itself for almost 10 years, it's really hard to reject that there might be something wrong with Dec exams.