QGIS3.ini might list plugins that not installed anymore.
File system might have plugins that are not (yet) listed in QGIS3.ini.
Ideally the list would show all plugins that are installed in the profile judged by the file system as actual truth.
It would be a fantastic side-quest to list plugins that are referenced in QGIS3.ini but do not exist in the file system and offer the user to remove those entries. This would require special handling though. If you plan something like this, consider tracking it as a separate ticket and feature.