It's specifically because there are huge numbers of people watching this carefully and trying to do that that it is irrational on the margin to try to do so.
This, it's not 1940 anymore, the average Joe can setup an investment account in 5 min on his phone and heard his buddies talking about "buying the dips is a foolproof way to become a millionaire".
As an example I saw a lot of discussion about buying the drop of Boeing stock, about 1 month after the 737-max were grounded, expecting things to be back to normal and a quick rebound. People who bought it at 370 now have stock with about 230/share... And still dropping.
