How can they artificially create a monopsony? By talking secretly to each other? It seems to me that if there is a real need, then they would have a hard time doing that.

Take software developers - if it is still true that they are still in high demand. How would corporations go about creating a Monopsony for software developers? Stop producing software? But if software is in high demand, how would they be able to prevent other companies starting up that develop software?