Why mostly dp internal auditors play a checker role rather than a Controller?

This is as per TORs of Internal Audit to identify weaknesses and point them to management. Internal auditors can identify problem/weakness and can suggest its solution. But the implementation of that solution is the sole responsibility of the management. 

Thank you for the invitation.

One of the Internal Auditor prime responsibilities is to assure the work procedures in a proper method as stated in the profession rules and company process rules. 

Because the main purpose of the internal audit is to inure that all the procedures is complying with the entity polices