IPMI is painfully insecure, and therefore assumes the existence of a completely separate, protected network. Some people don't colocate more than a few machines (and therefore can't justify the extra infrastructure for an IPMI OOB network), don't want to pay extra for a colo provider to provide IPMI OOB, and/or don't trust their colo provider to have access to such a sensitive and insecure thing.

Having an emergency method to connect is an excellent idea.