I cannot tell if or when the functionality is added to workspace, but the reason why it is different from repos is probably because with repos you actually make an external storage (git) the master of the files.  Whereas Workspace from the very beginning is built as being an entity on itself (with no/little git integration), an api etc.
Reworking all that to have the same functionality is a lot of work. 
There were several requests to have decent source control options using git.  So Databricks added functionality, without modifying an existing (working) part (Workspace).