The zzergs did not want humanity as slaves. They did not want earth's raw materials. There was no strategic agenda. They believed. They knew that they were alone and that none of us should be. Unfortunately for the rest of us, they were wrong, but this was a temporary illusion in their eyes. Humanity was a mass of clamoring animals in their directed energy beams and all reasonable objections in favor of man's existence were short lived.
In the panic that followed their arrival (a 30 mile wide greeting card of radioactive "sunshine") some engineer recalled that there was a single shuttle in space. The U.S. had directed great effort at placing a few relics of man kind's existance on the orbiting rock. This astounding effort produced little more then an astroid in the eyes of the zzerg and as such went unnoticed. Th engineer sent the sum total of mankinds knowledge, wikipedia.zip, to the lonely man made asteroid before being burnt alive with the rest of Houston.