It causes slow down problems. It’s siloed. It’s out of your control often. That’s why you have a lake/warehouse.

The “fact” vs “dimension” table is just one way of database design. You can have facts and dimensions in a source system. You can have them in a reporting layer. Like darzog said, if you have a dedicated reporting layer with certain business logic built in, then you’ve created a source of truth. You don’t want everybody asking the same question to be building their own answer with their own assumptions.