What are the advantages of collective bargaining for an employer?
(I am being serious - I really want to know).

The only one that I can think of is where the nature of an industry is such that the Basic Conditions of Employment Act provides a significant obstacle to the adoption of a particular employment practice. In terms of the Labour Relations Act, a collective agreement may set terms in "contravention" of the BCEA - as long as it's agreed by both parties in a collective agreement.

But there are companies and industries which seem to willingly enter into collective agreements, even when this "benefit to employer" doesn't seem to be in play.
So what am I missing?
What other possible benefits for the employer might there be?