Why do some companies implement a policy to require all employees to wear a uniform, even though some of their employees aren't visible to customers?

It is for the uniformity of the company and to establish the brand image and in fact it shows the organization's care & uniqueness towards the employees appearance.

A few of the reasons are also to maintain the companies policies & for safety reasons too.

Among the factors that make the company in its system of internal procedure are the primary priority protocols that depend on the features which give it a good impression and good improvements

It is an Expression and moment of truth.

Uniform dress is a real, virtual translation of belonging

Equality within the employee workforce wich in turn strenghtens its deliverance.

Other reasons may include brand name, safety, country laws and for better coordination.

Company uniform is one way of showing our loyalty to our company.

Whether we are visible to the customers or not it is right to implement policy

strictly. 

Yes. Being in uniform creates in the mind of customers about the true essence of unity or solidarity. 

So that the compay can easily regulate and identify the defaulters in the Companies regulations and instructions, promote the good image of the Company and differentiate the Company from other competitor's Companies.

To give an impression for Unity of purpose, Commonality of cause, sense of belonging and feeling of pride & prestige to the employees 

Implementing Uniform to employees have following advantages to companies.

1. To create an image in employees mind that all are equal and there is not discrimination with clothes.

2. For Security reasons. To identify their employees.

3. Create loyalty among employees towards the company.

4. Free publicity of company image in market.

5. It increases brand image in market