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.
it's perfectly fine if people are afraid to invest in crypto as there are many reasons to be afraid. Proper education should go first, only then the investment should follow.