The reason is those people who start panicking when Bitcoin starts dropping its price are not real traders but noobs who easily panic and get FOMO, and that's why they start selling their Bitcoin at a loss.
Bitcoin never devalues itself, and all people know this point. Its price decreases due to changes in the market like news, etc., which cause this drop. But soon, Bitcoin regains its original value, and sometimes it surpasses its previous target. So, don't be foolish and sell your BTC; instead, wait for the price drop and buy some more because it's a chance to buy BTC at a low price.