Because greed let people keep on waiting for higher and higher value for there coins and end up selling at dip.
Since price can’t go up all the time.
I am also one of those notorious holder and i often regret that i have not sold my coins earlier but i also have a reason why i want to hold my coins for at least 1 year. When i have them in my wallet for 1 year then the potential profits are tax free if i sell them before the 1 year time frame then i have to pay 25% taxes on the profits and i just want to do that. Of course this decision has cost me some significant profits because back in the beginning of may my portfolio had more than 5 time the value than it has now and if i had sold back them my profit would have been a multitude higher even with taxes, but i don't care.