The Cybermen have always been a race on the edge of extinction. In their very first story their home planet of Mondas was destroyed. Their third story would introduce us to their adoptive home of Telos and their tombs, a sign if one were needed of the Cybermen’s apparent weakness and indeed possible extinction.
In Revenge of the Cybermen it’s clear that they were thought to be utterly destroyed, an echo of their second story, the Moonbase.
There were Cybermen, every child knows that but they were all destroyed ages ago
You’ve no home planet, no influence, nothing! You’re just a pathetic bunch of tin soldiers skulking about the galaxy in an ancient spaceship!
When the Cybermen returned unannounced and unexpected in ‘Earthshock’ it seemed that they had been working to restore their strength and ready to exact their revenge (an odd concept for a race without emotion granted) on humanity for their many defeats.
Attack of the Cybermen returned us once again to Telos and tried (and mostly succeeded) in tying together the events of the Tenth Planet, the Tomb of the Cybermen and the Invasion.
Silver Nemesis, in a similar fashion to Remembrance of the Daleks seemed to imply the outright end of the Cybermen, and when they returned in the modern era it would be in a parallel dimension and created on that alternate Earth (referred to Pete’s world).
To add confusion it would later be implied that there were two sets of Cybermen, from Pete’s world and our own Universe.
The only time we have really seen the Cybermen in a position of power was when Rory encountered them to deliver a message from the Doctor….. and even then mass destruction would ensue.
All of these examples serve to show us how the Cybermen, despite their augmentation and removal of emotions are driven by fear. Fear of extinction, fear that they will not survive, a trait shared with all life.
Of course the Cybermen can’t procreate, they are reliant on conversion of other humanoids to become like them. Often driven to hide from the Universe until they can return to a position of strength and ready to return to make us like them, and survive at all costs.