Almost all Colossus-conquered cities had their Teleport Platform shut down to prevent any human cities from being able to spy and infiltrate them. The Colossuses weren't stupid enough to let such a big threat open.
However, what the Colossuses failed to realize was that they might be clever themselves, but their subordinates might not be that bright.
Just because one formed intelligence didn't mean they had the wisdom to understand what and how to use their knowledge to their advantage.
The orc in front of Xu Feng was precisely what it meant to be intelligent, but lacked wisdom. To be blinded by momentary greed and agree to his request, the orc actually opened up a door for the human cities to infiltrate successfully.
As the main contributor of this, Xu Feng couldn't even fathom the type of rewards and benefits that would await him.