Many of the challenges in management of IT projects belong to a class of problems for which a higher-order approach to a solution already exists in the form of a MIS theory. Management Information Systems (MIS) theories can be used as guidance for answering many of the important questions that occur for IT project managers. Despite this, many IT project managers underuse such theories in their management of projects. In this paper, we identify and explain the underlying reasons for the underuse of MIS theories by project managers in their management of IT projects. The underlying reasons that we identified include: (a) confusion around personal (specific-implicit) theory and scientific (general-explicit) MIS theory, (b) misunderstandings about the position of MIS theories among scientific theories, (c) the difficulty of gathering evidence and facts about the outcomes of using MIS theories in IT projects, (d) difficulties managers experience in choosing the right type of MIS theory for a particular challenge in an IT project, and (e) the ability or otherwise of current MIS theories to respond to evolving challenges of managing IT projects. The main audience of our paper is IT project managers and IT and MIS researchers.