A data cleansing or cataloging project gets your data to the right state. Data governance keeps it there. Governance means defining who owns data quality, what the rules are, how incoming data is validated, and what suppliers are required to deliver. Without it, data quality is a constant battle. With it, quality is maintained as a normal part of operations — not a recurring emergency.
From experience: organisations without governance structures reclean their data every three to five years — at the same cost, with the same disruption, and the same result.