Yes, I get it...Most CFIs are not active even though they have current certificates. But the same was largely true in the comparison year of 1990, wasn't it?
The "four times fewer" number I gave was a ratio of ratios.
[PPL issued 1990 / legal CFIs 1990] divided by [PPL issued 2013 / legal CFIs 2013]
This type of statistical analysis should eliminate the inactive-but-legal CFIs who were present very large numbers in both data sets.
Fact remains there are almost four times fewer students to go around. (Actually, 3.86 times fewer by my calculations, but 4 is close enough.)