Low Quality Code
An application or service is vulnerable when its security depends on a module upholding a contract that it does not uphold.
Most new software has bugs when first released. Over time, maintainers fix the bugs that have obvious, bad consequences.
Often, widely used software has problem areas that are well understood. Developers can make a pragmatic decision to use it while taking additional measures to make sure those problems don't compromise security guarantees.
Orphaned code that has not been updated recently may have done a good job of enforcing its contract, but attackers may have discovered new tricks, or the threat environment may have changed so it may no longer enforce its contract in the face of an attack.
Low quality code constitutes a threat when developers pick a module without understanding the caveats to the contract it actually provides, or without taking additional measures to limit damage when it fails.
It may be the case that there's higher risk of poorly understood contracts when a community is experimenting rapidly as is the case for Node.js, or early on before the community has settled on clear winners for core functions, but we consider the frequency of vulnerabilities due to low quality code in the npm repository roughly the same as for other public module repositories.