This can be seen two ways. Yes, the specialization of service and products for a particular illness has a cost associated with it. But, the cost of specialization is within the field not the direct cost of the insurer. The availability of many treatments/products does not directly relate to cost burden of the insurer as the cost is proportional to customer need. Increasing markets are most likely passed proportionally to the consumer based on risk.

The net increased of cost could be seen as a decentralized cost over their entire customer base. The question is... if the insurer is taking a relative percentage for each dollar passed between the insurer and healthcare industry then, maintaining a higher volume of expenses is proportional to their profit. (This would be dependent on a fairly non-elastic demand of people buying insurance). There might also be regulation associated to the maximum amount of profit they can make relative to the actual amount used to cover their customers. If that's the case, then more money spent is probably more money earned.