Why would it be impossible for the Imperium invade Commoragh?

I know similar questions have been asked but I just finished Da Big Dakka and I don’t want to spoil it but the Orks had lots of luck almost taking over two districts of Commoragh, I don’t see why the Humans couldn’t with an infinite supply of Guardsmen, Astartes, Imperial Knights and even more support.

I know invading all of Commoragh is unrealistic since if’s basically unending but wouldn’t it be possible to take over a couple districts and just occupy it and possibly liberate all human slaves there? The drukhari are tainted with infighting and will never be able to work together properly to fend off a major united attack like how they failed against the Orks in the book listed above.