system
Given the following post, respond as if you're commenting on Reddit:
human
[W40K] Why are ground troops still relevant?

Today, outside of territory occupation, most of the war is fought by drones, airplanes, etc; with ground forces being used only for small guerrilla style operations (special forces). Sure, a lot of troops are deployed to actually control land in hostile countries (eg occupation of Iraq by the US, or the current Centrafrican Republic deployment of the French). But where does it happen in W40K? If Chaos attack, wouldn't it be easier to bomb them from airplanes/spaceships than deploy thousands of guards and space marines? Same with Tyrranids, or Necrons, or pretty much everything else. If a large number of troops are deployed at any point, they would be bombed and destroyed easily.

edit: I was not clear. I am not talking about specifically carpet bombings or exterminatus, but if say a bunch of Chaos space marines deploy in a given place, wouldn't it be easier to send W40K F16s to deal with them rather than a large number of guards?
gpt
Firstly these drones sound an awful lot like AI which is a big no no. 

Your enemies also have spaceships so you cant really just perch and fire unabated. 

You might not want to destroy everything in that area. Retrieving a relic or securing a position doesnt always necessitate orbital bombardment. 

Its also about resources. The Imperiums greatest resource is the sheer number of people they can throw at a problem. 

They also do use orbital bombardment and Exterminatus... frequently. Shockingly frequently. Its just we dont hear about the heroic battle of Feral World C3498-Alpha because a ship pulled into orbit evaluated the situation, dropped a bomb that destroyed all life and called for a new settlement to be sent because the last colony started growing dicks on their heads from worshiping chaos.