Because Bitcoin investment is very important for a person and if you can succeed in the investment, your quality of life may change. It is not advisable to deliberately take risky steps in such an important matter. We must have a positive attitude towards investment and have proper plans against even the slightest negative possibility.
What you said here are so true, nothing is guaranteed when investing in Bitcoin, their are risk attached to it, but that risk factor can be limited if being held for a longer duration, so that being said, investing an amount you can afford to lose and not going all in on your investment is actually the best way to invest in Bitcoin, so that if it doesn't goes as planned, you wouldn't have to contemplate on committing suicide.
Although there are two possibilities of success or failure in investing without an emergency fund, the possibility of failure is still high. So we should not ignore the emergency fund in any way. We should not even be sure about the future, whether it is positive or negative.
I don't think that their is a possibility in you being successful as a Bitcoin investor as an average income earner if you have no emergency funds that stands as the last layer of protection against any unforseen emergency that may arise in the future, but for the case of the rich guys, they might have such leverage to invest without an emergency funds because they have rich father, uncle, friend's that can bail them out of emergency situation that may have warrant them to temper with their holdings, so if you are not rich, kills that idea of investing in Bitcoin without an emergency funds because emergency will surely comes in the future, and when it comes your Bitcoin investment is doomed if no emergency funds then.