Why do companies hire EXTERNAL "consultants" to solve INTERNAL problems?

the only reason for hiting external consultants is when they miss the problem solving (Experience or Ideas) withhin the firm itself.

When the organisation feels that their internal resources to handle a dire situation is not competent enough, then it is always better to involve an external consultant who are experts in solving such problems in organisations on day to day basis. consultants are basically good at what they do as they are experts in their field. 

Becasue, they get, opinions which are free from any influence and influence is the biggest threat for any industry.

the biggest companies do this procedure to light burden of this problems from the management team And to secure this time for solving internal problem to work instead.