Schemas require domain knowledge. When domain knowledge is unclear or lacks ownership, it can lead to a range of issues that impact both data integrity and system functionality. Things that screw this up in the financial world include: working in different countries, acquiring new branches, new hires, and leavers. And people who think they can insist the database schema be protected somehow. A manager told me to add the last reason, it wasnt my idea and makes little sense.

With a database you can lock down the schema. In reality though, many data system are composed mainly of people emailing in Excel spreadsheets. Good luck enforcing any sort of schema there.

My day job is writing a desktop/file-based ETL system. I have just added in a schema version feature to cover these sort of issues. It was one of the most requested features, because most people aren't able to control the schemas of the data they receive.