Yes, shields exist plus there's also tons of underground areas. But it still doesn't change that even their idea of WW1/WW2 in space gets incredibly fucking dumb at times(it's not as if anything else they come up with is some great literary work, it's all pulp schlock).I can at least see why there's not a lot of massive bombing campaigns in gw's book simply due to the fact that void Shields exist over large Hive section so you really can't bomb something when someone has a massive void feel they can just block most of your.
even though I enjoy the ghost novels it really annoys me when Dan abnett forgets grenades are a thing.
for some reason the Imperial Guard is incapable of working with the Imperial Navy because angry shouting matches.
none of these people have ever picked up a book on combined arms Doctrine or a single book on Modern Combat
I think the biggest reason for their lack of actual combined arms and modern combat, is again their focus on everything being early 20th century warfare in space with the bulk of it really being ww1. Close air support wasn't really a thing, maybe at best you'd be able to get some naval guns shooting at coastal targets, but beyond that it was mostly a ground campaign. Unfortunately I think if GW did ever bother to have their authors write anything resembling modern 21st century combat doctrine, we'd get even more bitching from the fanbase about it.