Technical debt leads to low morale

Most developers want to work on greenfield projects where they can develop new features, rather than to inherit legacy brownfield projects riddled with bugs and technical debt. This will likely reduce the morale of the developers.

In some cases, those working on brownfield projects may even show animosity toward their colleagues who work on greenfield projects. This is because newer frameworks, libraries, and paradigms will eventually replace older ones, making them obsolete. Those working on legacy projects know that the skills they develop will be worthless in a few years' time, making them less competitive on the job market. In comparison, their colleagues are gaining valuable experience on more modern frameworks that will increase their market value. I can't imagine a developer being happy knowing their skills are becoming less and less relevant.

Furthermore, having technical debt would likely ignite disagreement between developers and their managers about the best time to repay the debt. Typically, developers demand immediate repayment, while the (inexperienced) managers would try to push it further down the line.

Overall, having technical debt in the project tends to lower the morale of its developers.