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.
Only those that have a very solid record of obtaining constant profits can entertain the possibility of becoming professional traders, if you are one of the few that can do that then congratulations you are going to make a lot of money in this market but most people cannot get those results and they need to accept it.