I believe the whole point was that these regions weren't strategically valuable at all. Few resources, nomadic tribes who would raid your trade routes or settled areas, and long travel times from major trade centers were all reasons why few empires desired to own the steppe. Plus nomads have no homelands which they would hope to defend and so it was almost impossible to come to grips with a nomadic army in a pitched battle unless it was on their terms. Therefore regions were highly difficult to control.