"In the United States, total stock listings peaked at 9,253 in 1997" & "Europe’s equity listings peaked in 2007 at 14,008" - these two points indicate that the peaking of the number of listings, on an uptrend, was cut down by the financial crises. So I believe it is the economic situation forcing companies' bankruptcy and the restructuring through M&A seems to be more likely reason. As for the companies taking a private route than being public should have resulted lesser growth rather than decline.

Thanks Jason for this lovely insight!