Dolphin is Plasma™'s default file manager. It aims to improve usability at the user interface level. Dolphin focuses only on being a file manager whereas Konqueror, which was KDE's default file manager in KDE 3 and can still be used for file management, is a universal viewer for many file types.
This design approach allows the developers to concentrate on optimizing the user interface for the specific task of file management.
Please report any problems or feature requests to the Dolphin author via the bug report dialog. This is accessible either from the button at the right of the toolbar in the default mode without menubar; or from → menu of the application, if the menubar is shown.