Why might a corporation use the cost method of recording an intercorporate investment while using the equity

Question:

Why might a use the cost method of recording an intercorporate investment while using the equity method or consolidation for reporting?

Corporation
A Corporation is a legal form of business that is separate from its owner. In other words, a corporation is a business or organization formed by a group of people, and its right and liabilities separate from those of the individuals involved. It may...