Previously, issues were reported to Apple, who then had to vend them back to their data sources (TomTom amongst others). It was up to the data sources to implement the changes.
Now, issues reported to Apple can be immediately acted upon, or compared to other data, or reviewed by employees, or even can be marked for validation during another "drive-by".
> "There’s also the matter of corrections, updates and changes entering a long loop of submission to validation to update when you’re dealing with external partners. The Maps team would have to be able to correct roads, pathways and other updating features in days or less, not months. Not to mention the potential competitive advantages it could gain from building and updating traffic data from hundreds of millions of iPhones, rather than relying on partner data." from [0]
[0] - https://techcrunch.com/2018/06/29/apple-is-rebuilding-maps-f...