One major reason that can make one not invest in the long term is not having a steady income source or another source of income that is at least generating income too. Imagine when you don't really have any sustainable income sources and you manage to get some funds and invest in Bitcoin. You will just be able to hold on for some time, and any day your daily wants are not met and there is no money on you. In such a case, if your investment happens to be the only money to save the day, you will not hesitate to sell off. Also, just as you stated, health issues are another major reason why someone might not hold on for long, depending on how critical the situation is, and if they don't still have another source to get the money for their medical bills, they will just sell their asset if that's the only option.
You are right in there. You cannot expect to invest for long term if you don’t have sustainable income in the first place. That is why never go for investment first but look for a stable job that will provide you sustainable income. That way, you will never compromise your investment because you suddenly fall out from your own budget. Investing and long term hodling are essential into one’s life, but everything will not make sense if you are also struggling providing food on the table. So know when to invest for good.