These are:
1. Volatility of the Market.
2. They don't have the knowledge about crypto.
3. Negative news that they see or hear in social media/TV Media.
4. They were scammed and afraid to invest again.
5. Threats of hackers in the internet.
But users can also protect their computer from hackers by using:
1. Virtual Private Network for Internet Protocol
2. MetaMask Wallet
3. Not saving any private keys in your PC.
I agree on all the items listed, but what makes me think this time, is that the community is still lack of knowledge when it comes to crypto currency, this is one of the reason why some people never invested in crypto, that is why i support to have a college course pertaining to blockchain and crypto education, so that it could be shared to students and so that the general public could be informed.