Investors lose money because they enters and exit the market at wrong time, poor financial management and also lack of proper knowledge related to assets they are all investing.
Entering and exiting the market can easily be solved because you just need to be good and smart at trading. Poor financial management can be learned too. I think there's a reason that everyone can't avoid and that is the fact that trading isn't for everyone.
It is a need for us to think not only the positive things but also the negative ones as I see that most of us are neglected to do that nor it comes into our mind due to some excitements. I could say that not all investors are knowledgeable, they might just encourage to invest in crypto as maybe one of his/her friends tell them but they are not able to tell the truth about crypto. In this case, it was not a big surprise why we lose, to come into the market without any knowledge is just like suicide.