I can imagine that you've never worked in a large scale development studio that runs multiple departments.
You don't just "Share" resources from one department to another, If the WOW department wants to use the WC3 engine, they have to "BUY" the engine from the WC3 department.
Granted, the "BUY" is on paper only, but you need to accurately assess the total development cost of a product, and if you're taking software from another department without paying for it (Someone paid for it originally), you do not have an accurate cost assessment.