Presumably, the manager has other property he is managing or perhaps has some other business interests? For example, maybe he has an office off the named insured's premises where he conducts other business. A customer comes into that office and trips and falls. The manager is going to need his own general liability coverage for any resulting claim. Or, perhaps he wrongly evicts or invades the private occupancy of a resident in some other property. The named insured's liability policy will not apply since the real estate manager is not an insured under such circumstances.

So, there can be some situations where the manager is on his own when it comes to liability questions. His duties and possible other work would have to be examined to see if there are any circumstances where he could be not acting as the real estate manager of the named insured, and thus, would need his own liability coverage.