Well some people don't have the time to do that and they only want to put some money and wait for some time until their investment bear result, it is indeed more profitable if they can trade between the holding period if there's opportunity. I have some coin for long term investment but i also have fiat ready if there's opportunity because i also trade some coin.
Day trading can be extremely profitable, this is something that anyone that has spent any time in the market knows, the problem is the huge amount of time that you need to invest into it, if you have a full time job then it is very unlikely that you are going to have enough time to dedicate to day trading, so it is not really a surprise that one of the most popular methods to try to make money in this market is to hold your coins for the long term.
That method may be not working anymore. Cryptocurrencies are mostly speculative assets, and they had been growing until the market became saturated. It became saturated as no new money was thrown in, and then prices expectedly crashed because most people involved in crypto were there exclusively for profit motives. In other words, holding was one of the most popular methods to make money in crypto while crypto was rising for so many months.
But these days may be over. In the majority of established markets, both purely financial and related to commodities, holding is meaningless, and you can only earn something by actively using your brains (if you have them), not by sitting idly on your hands waiting until the price rises enough to let you grab easy profits. This was a unique opportunity, and I'm not sure it is going to present itself again in the future.