This site limits the number of login attempts for security reasons. If a user tries to login and fails 5 times, they will be locked out and an Administrator will need to unlock their account before they can regain access. Options can be changed under the Settings > Limit Login Attempts tab in the WP Admin. Recommended settings include the following:
To learn more read the WPBeginner Blog article: How and Why you should Limit Login Attempts in your WordPress.