Exam CISSP topic 1 question 357 discussion

An organization's internal audit team performed a security audit on the company's system and reported that the manufacturing application is rarely updated along with other issues categorized as minor. Six months later, an external audit team reviewed the same system with the same scope, but identified severe weaknesses in the manufacturing application's security controls. What is MOST likely to be the root cause of the internal audit team's failure in detecting these security issues?