I can see why you’d call out agile as a common cause, but I’ve seen as much (or more) tech debt in teams with waterfall or waterfall-like methodologies.

I would call out anti-patterns and architectural flaws/gaps as the ultimate enabler for unintentional technical debt. Especially in OOP code where, as unique and smart as we all think we are, most of us fall into the same anti-patterns that are quite typical.