Why do employees always blame "Wrong policies" instead of getting it corrected if it's wrong, how we can motivate them to do so?

We can start by properly educating the employees about the policies then regularly trying to check awareness and their feedback about certain policies that may not seem to work. Motivation will surely follow if the employees felt that their opinion matters. It is a joint effort between the management and the employees to determine what will best work for the company. 

Conducting a proper orientation regarding the rules and regulations of the company and explaining to them their job description will give them knowledge regarding the company procedures.

To keep an employee motivated, a proper training, follow up training, follow up orientation and giving them a positive feedback regarding performance will motivate any employee because we show them that we care. 

Employees who blames the policies does not have adquate knowledge about it.  By effective communication, employees would know more about the polices, what's in it for them and the company. To help them, management team should reach out via effective meeting or forum to discuss and come up with fair decision/knowledge if the policy cannot be changed.