No single decision creates route debt. It is made of reasonable choices that were correct on the day and never reviewed afterwards.
Why it matters
Debt is why operations get harder as they grow rather than easier. The route book carries years of one-off accommodations, each invisible, together adding miles and minutes to every week. Eventually dispatch spends its day working around a structure nobody designed, and the business concludes it has a software problem.
How you notice it slipping
Nobody can explain why a particular account sits on a particular day. The number of manual adjustments per week rises year over year while the account count rises more slowly. Experienced dispatchers are valuable mainly because they remember the exceptions.
What to do
The tell is how people talk about the schedule. Where debt is low, dispatch explains decisions with rules. Where it is high, every explanation is a story about a specific customer and a specific week, usually from several years ago.
Repay it on a schedule rather than in a crisis: one hour a week spent returning drifted accounts to the lane they belong in. The work is unglamorous and the effect is cumulative, which is exactly why it only happens when someone puts it in the calendar.