system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel and DC comics] Why haven't humans begun to colonize other planets yet, they seem to have the tech for it in both universes?
gpt
In Marvel they've made forays into the Negative Zone, which is a goddamn nightmare. As far as other planets, you've got to deal with the multitude of alien races that want Earth exterminated. Once you get outside our solar system (Which is in a contested territory between Kree and Skrull space, hence the invasions) you're going to be in enemy turf. Either the Shi'ar, the Kree, the Skrull, the Badoon, The Dire Wraiths, The Phalanx and et cetera. 

In DC it's kind of the same deal except there are literally THOUSANDS of other alien races out there and a lot of them really really hate Earth in particular. You've got the Khunds, the Durlans, The Manhunters, Thanagarians, the Okaarans, The Dominators, and on and on and on and on. And thats not including the various Lantern corps.