One of the underlying themes of the work we do at Net Objectives is, Agile by itself is not enough. Agile needs something that connects the transformation of the team to the activities and concerns of the larger organization. Nowhere is that more clear than technical debt. You need to nestle Agile within a larger operational approach, such as Lean, to deal effectively with a problem like technical debt.
One of the reasons why organizations accrue technical debt quickly is that they don't see it as a systemic problem.