There are two primary reasons why storing your private crypto keys in the cloud is a bad idea. First, your cloud provider represents a centralized honeypot that could experience a security breach, allowing cyber criminals to access your data. For example, in August 2018, a fourth man was jailed in the U.S. for hacking into private Apple iCloud accounts and leaking nude photos of Jennifer Lawrence, Kirsten Dunst, Mary Elizabeth Winstead and others. So it does happen. And it will probably happen again in the future.