I think you're mixing up compromise of an account with compromise of the data associated with that account.
If a particular piece of data is accessible to people of a dozen accounts, compromise of any of those accounts potentially compromises the data. That's a legitimate concern for people who want certain data secured, whether other accounts with access are also secure. In some cases, it may be best to have an authentication policy that provides a baseline level of protection even for the most clueless users, rather than a system where you're able to secure your own account.