What is a major risk of reusing the same password across multiple accounts?

Reusing the same password across multiple accounts significantly increases the risk of unauthorized access to all those accounts if a single password is compromised. If an attacker gains access to one account through a security breach or phishing attack and that password has been reused on other platforms, they can easily gain access to those additional accounts without needing to break into them individually.

This practice undermines the security of multiple accounts, as the breach of one can cascade to others. Therefore, having unique passwords for each account acts as a barrier that helps contain potential breaches and protects user data across platforms. The other options focus either on convenience or issues not directly related to security risks, making them less relevant to the question.