Windows 8.1 and later versions of operating systems has co-installer integrated into the OS kernel.
So, If the driver is targeted to windows 8.1 or later versions the co-installers are not necessary.
Please check KmdfLibraryVersion in the current driver package .inf file which you have. If the version is 1.11 or lower then a WDF co-installer is needed, if the version is 1.13 or higher then they are not needed:
kmdf version 1.13 will run on windows 8.1 or later.
kmdf version 1.15 will run on windows 10(TH1) or later.
Thank you for the explanation !