Developers are known to keep third-party dependencies of their projects outdated even if some of them are affected by known vulnerabilities. In this study we aim to understand \emph{why} they do so. For this, we conducted 25 semi-structured interviews with developers of both large and small-medium enterprises located in nine countries. All interviews were transcribed, coded, and analyzed according to applied thematic analysis. The results of the study reveal important aspects of developers’ practices that should be considered by security researchers and dependency tool developers to improve the security of the dependency management process.