Because Ghost is not going crazy with solos, screeching/belching/barking lyrics out, isn't recording their material in some hollowed out and echoed building somewhere. They also aren't catering to lyrics about how it'd be a wonderful day to be devouring some flesh and fucking the eye sockets of a skull. But you wouldn't know that with the vocalist doing said belching/barking/screeching lyrics until you read what the song is about.
So basically, Ghost is not liked because it's not catering to metal edgelords.
The downvotes prove me right. :)