Because it's been chopped up for future DLC. DUH...

Have you seen the shape of them ?. They are so round and fat I'm surprised they can walk ten yards let alone invade another planet. They would seriously need to get in shape before they did any invading! Forget the Cambridge Diet they need the Cabal-ridge Diet!!

Rasputin the last warmind (and strongest of the warminds) is what keeps them from blowing earth up. Rasputin's defense network keeps fleets at bay. That's why the cabal, fallen, vex, and hive are all trying to break and control Rasputin.

What the hell do the Cabal eat, anyway? Doesn't seem like a vast variety of options on Mars. Let alone, they're rather large in size. [spoiler]Have a snickers. No one likes you when you're hungry?[/spoiler]

It is VERY likely that all the alien ennemies (wheter they're fallens , hive , vex or cabals ) are looking for something very valuable in our solar system . I heard somewhere that one of the ultra cabal we have to kill shows a lot of interest for humans' golden age technology etc. I don't remember whether it was Dinklebot saying it or a grimoire card . In fact , I believe the reason why cabals went to our solar system was to vanquish the vex . Maybe they were looking for a way to access the black garden (which has been hidden in another space-time continuum by the vex) . Destroying Mars would prevent them from finding any possible way to access the black garden . However , it is stated that they are prepared for this eventuality . That is why the psion flayers brought Phobos so close to the marsian surface . It is suspected that they could crash it into the red planet as a weapon of mass destruction (hopefully PSN players killed those -blam!-ers ... many times). Also , it is said once that humans and cabals were never meant to fight each other . It is said that it was "accidental" . Then , we also know that the Hive wants to hack Rasputin . They might be looking for something on Earth too . Who knows , there might be a dimensional wormhole in Earth that would allow them to access Oryx , just as they created a gateway in the Hellmouth to access the dimension in which they saved Crota's soul . Concerning the fallen , it simply looks like they're a bunch of space pirates who found some viable planets to set a camp on . When you think about it , everytime there is a fallen related public event happening , you see those gigantic ships teleporting and flying over your head , not giving a flying -blam!- about you killing the dregs they send on the ground . They could probably just fly to the City , shoot a bunch of rockets and kill every single human remaining on this planet . However , it is also possible that they are looking for something on earth . Then , regarding the Vex , they are probably the most powerful ennemies we have to face . Afterall , they have the ability to simply erase the existence of anything or go back in time to correct their mistakes (if they ever make any) . Well at least , they can do this within the vault . They are probably also looking for something on Earth or at least in our solar system , something invaluable that they cannot recreate . However , at lot of mysteries remain regarding the vex's intentions . Afterall , all it took to kill their god was to kill three gate lords and a bunch of goblins . Coming from a omniscient almost omnipotent hive mind , I'd have expected more resistance . So in the end , my theory is that the traveler is not as nice as we think . It might be hiding something , something that is coveted by various races across the universe , something valuable enough for them to travel for eons across the universe , something valuable enough for the traveler to sacrifice itself in order to protect it . I really hope we'll find out more about that in Destiny 2 or int the next DLCs

If they exploded Earth, they would explode the Traveler too, because the Traveler is on Earth. I think that the Darkness doesn't want to kill the Traveler, they want to infect it. Like in the moon mission, they were "draining the traveler of its light". The darkness wants to be able to control the travelers power.

Sorry for the shirt reply to your long question but. Mars: They are searching for something. It's stated in the missions. Something to do with the warminds. And they are looking for something vex related. Read the Grimore card for the crucible map Bastion. It's pretty funny. Earth: Rasputin is protecting it and I believe the cabal scared of it. There is a ghost fragment from a hunter where Rasputin tested one of his weapon systems on a cabal patrol that were engaged in combat with the vex on Mars. Rasputin left the cabal shitting their pants and frantically calling for back up.

Rasputin is the answer. He's a super a.i. (Skynet anyone?) He's got doomsday weapons. [i]He's Russian.[/i] 'Nuff said

Did I already comment on this? If not: 1: the Hezen Protective are holding them in a stalemate 2: they are likely looking to conquer everything 3: they are running from something, destroying places to hide isn't a smart option 4: this is the beginning of a long lived videogame, and all life threatening plots have yet to be unraveled. The Psion Flayers have pulled Phobos out of orbit, and are waiting to use it as a Weapon. Expect that to be a plot point in later games.

Rasputin + The Array = Protection

We could just blow up the Middle East. We have the means to do it, but it's probably not the best strategy.