Teleports were complex machines that required the best available technicians and scientists. After all, a single miscalculation could maim or worse anyone making use of those machines.
Things worsened when it came to evolved warriors. They didn't only require far higher amounts of energy so that the teleport could activate. Those machines also had to adapt to their specific existences to avoid problematic interferences.
Obviously, Khan exemplified those complications. His return to Earth wouldn't have been so delayed otherwise. Zedekiel had technology suitable for existences at his level, but it had taken time to prepare them, especially since the Emperor was with him.
Even then, Khan and the others had to cover the last stretch of the trip by ship, delaying their arrival to Earth even further.
