Whilst it would seem implausible that they are all generally designed to for the ease of use of a human, the explanation is simple. Many of these societies are the descendants of humans who were carted across the galaxy as slaves thousands of years ago by the evil race called the Goa'uld. By liaising with these races and learning from them, Earth too has begun to create its own futuristic technology. All such technology is SCI-classified top secret, and is used solely by the SGC and its SG teams, or in Atlantis.