Because they are traders, not holders. Every trader panics including most professional ones, they are not bot. If you panic and sell your coin, you might be trader but not definetely hodler.
I am sure that an experienced trader deals with different types of trade. This is short-term, medium-term and long-term trade (the same hold). There is one more separate category of traders that HODLing (Hold on for dear life) 
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