Why do stock markets bears in the US always pop out of the woodwork whenever there's a pullback in equities

Why do stock markets bears in the US always pop out of the woodwork whenever there's a pullback in equities? Betting against US equities has rarely paid off from a historical standpoint, yet it seems like there are just as many bears as bulls these days. Yahoo Finance posted a clip today from yet another bear who claims valuations are worse today than they were before the dot.com bust. His claim is that the dot.com bubble was driven by a few names while today's overvaluation is driven by the entire market. Nevertheless, the same article mentions the S&P 500's forward P/E ratio is just 15.1. That's hardly an outrageous number. Bears also argue that earnings are at record levels compared to GDP, and this relationship tends to mean revert. However, couldn't that just mean other GDP contributors are going to rise? (VIEW LINK)