AWS Glue makes it easy to get a PySpark pipeline running quickly. It is significantly harder to build one that stays maintainable as logic grows, performs reliably at scale, and does not quietly accumulate operational debt over time.Most Glue pipelines start simple and become difficult to manage gradually — formulas get hardcoded, modules grow without boundaries, output files proliferate, and before long a single job is doing too many things in ways that are hard to test, hard to debug, and expensive to change.