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.
The markets have a tendency to move in two different ways, the market can be trending, which means that the price is moving in a very clear direction, whether that direction is up or not is irrelevant, the other way in which the market moves is called ranging which means that the price is moving between a particular range of prices without a clear direction.
In the current circumstances of the market we see that the price of bitcoin over the long term is not moving much, so the strategy to take right now is to trade, if you really want to make money out of your investment, but as I said not everyone has the time to do that so they prefer to hold even if that is a strategy is not the best to do right now, but when the market is trending holding is by far the best strategy.