As an example, with Java, this weakness might indicate cycles between packages.
This issue makes it more difficult to maintain the product due to insufficient modularity, which indirectly affects security by making it more difficult or time-consuming to find and/or fix vulnerabilities. It also might make it easier to introduce vulnerabilities.
This issue can prevent the product from running reliably. If the relevant code is reachable by an attacker, then this reliability problem might introduce a vulnerability.