TPA Adding Plan Sponsor to E&O Policy as Add'l Insured

Plan sponsor is getting push back from new TPA about having the plan added as an additional insured to TPA's E&O Policy. According to TPA, the insurance broker does not permit the plan to be added as an additional insured.

Any thoughts on whether this is common practice?

Why would the plan be insured under the TPAs E&O?  Its there to protect the TPA against claims, not the plan...

The plan administrator/company needs to be covered under their own corporate E&O since they are employees of the company, not the TPA.   Why would the TPA be willing to take on the  liability of the plan sponsors actions (Since we all know that the plan sponsors sometimes do what they want outside of TPA advice)