Incorporated vs private pension companies

I notice that incorporated insurance companies like Prudential, Northwest Mutual and John Hancock like to use captive agents and brokers as their main distribution channel/s.

Private companies like Metlife however have 6 channels and almost 25% of their FYP goes to general agents (PPGAs).

Is this because incorporated companies must answer to stock owners who see the use of an independent agent as a loss of company profits (they have to pay higher commissions to independent agents)?

The private companies must answer to their customers however. This would mean keeping policy prices low making other channels more sensible.

Please tell me your thoughts on this...