~ Why so people hold rather than sell and buy again when low
It's because they know that in the future the price will be more expensive and higher. It's a matter of investing and just like any other assets that we know of, we don't want to sell it at a lower price. Holding requires less effort than being that type of buying low and selling high at most types and this is what traders do, trading and investing still have differences.
Yes You are right but sometime When investor buy in low and sell in high after selling price will pump again and it will create panic the investor buy again and price will goes down this will not much Profitable for all Investors i think that was also a reason for people HODLing