Health Issues: Health is wealth, which means without health a man is not wealthy. If there is any sickness that needs money for me or any member of the family to seek medical help, I might decide to sell some of my bitcoin holding to cover the bills. It is only the living that can enjoy the benefit of any investment.
Loss of source of income: A loss of a job or business might force me to sell some of my holdings if I exhaust all my savings. I and my family needs to be alive to enjoy our investment, so we need food and other basic needs to survive. it will be painful but it will be better than begging or taking loans.
Both of these reasons aren't enough for me to sell my Bitcoins... or I might depending on the reasons.
Why?
Because I have emergency funds that's enough to cover these 2. For Health Issues, I think I've had enough money that's I have been saved to cover enough, but if the worst thing comes where it wasn't enough, then I might sell a portion of not just my crypto holdings, but other assets as well to cover the bills. As for the Loss of income source, like I said I have emergency funds that's enough to cover me at least a year even I don't have any income source. I think that time horizon is enough for me to find another job.
Business opportunity: Many people in my country are migrating to developed to seek better employment opportunities. Many of them are cheaply selling their properties and businesses. If I have the opportunity to buy a cheap house or business, I might decide to sell some of my bitcoin because the profit from the business will help me to buy more bitcoin in the future. House rent is expensive in my country and it is really taking a large chunk of my income. If I own a house, my house rent can be used to buy more bitcoin.
This isn't applicable for me since I'm not a business-minded person, but for sure, there are some who already took some profit and sold some of their Bitcoins so that they will have money to be used if they want to make a business.
Unfavorable government policies: If the government of my country decides to ban the holding or use of bitcoin, I might be forced to dispose of them. I will not want to be hiding from law enforcement agencies or risk being arrested. I don't wish this to happen but if it does, I will have to take that hard and painful decision.
We in our country are quite lucky that our government is just neutral on cryptocurrencies.
What I mean is that, we don't hear any positive things on him that is related to crypto, but at the same time, we aren't hearing any negatives as well unlike in other countries where they are imposing a ban to use cryptocurrencies.
In summary, there are just two broad reasons that will make me sell my coins, first emergencies such as sickness and loss of a source of income, and better opportunities that will give me more financial backup to buy more bitcoin.
Same as you, I also think that the 2 options that you said are the only reasons why I will sell Bitcoins, but overall, selling Bitcoins is my last resort in case I'm in need of money. Maybe my only concrete reason as to why I will be selling my Bitcoins is to just take profit, re-invest or buy something that will generate me more money.