One of the factors is the fear of losing money since cryptocurrency price are not stable and most still fear the ban by their countries since government has not officially declared it legal.
Most people are not willing to invest into bitcoins for just one reason only and that is because they dont know a single thing about the whole issue with how buying something that is not tangible going to make them a lot of money.
I actually believe that most of the people who cannot invest even though they have money to invest are afraid because they are coming from financially conservative mindset which stops them investing cryptocurrencies.