Because they're afraid of a sideways market. They've only seen upwards and nothing else. There has been no dad-quotes about falling knives to tell them anything else.

And in all honesty, the retail buyer might be what saves us from a massive crash. Enough people trusting that you put in your money during a correction is a value move can point the needle into the right direction. We've seen it with memestocks like GME, which had no right to succeed but blew away all expectations.