1) Machine learning models can accumulate technical debt over time in the form of entanglement with other systems, unstable or underutilized data, and spaghetti code.
2) This debt can be reduced by isolating models, versioning data, feature engineering, and refactoring code into clean implementations.
3) As external conditions change, models may need to be rebuilt or modified to maintain accuracy since fixed thresholds and correlations can become outdated.