If unions are good for both the company and the workers why don't companies eventually implement the petitions of unions by themselves without any external pres

If unions are good for both the company and the workers why don't companies eventually implement the petitions of unions by themselves without any external pressure? You're making it seem like companies are too dumb to know what's best for them. I'm in favor of unions but that there's no doubt they can be detrimental to companies and to some of the workers, who maybe prefer more risk and higher rewards.