Of course that's their incentive. And because it benefits a few and distorts the market, collusion was made against the law.
So manipulating the market to artificially keep salaries low? Can you see the problem/illegality here?
It's silly how people view this situation here. If one company has the resources to manipulate the market, they will do so outside the talent pool. Apple could buy up most patents and restrict anybody from using them. THEN, you would see the problem. But when it's human resource, you want the free market to be free.