In many cases NIH occurs as a result of simple ignorance, as many companies simply never do the research to know if a solution already exists. But equally common are deliberate cases where the engineering staff rejects a solution, typically because they believe they can do better.
Many millions of man-hours and billions of dollars have been wasted as a result of NIH.
Original research about the NIH syndrome was by Katz & Allen, 1982, Investigating the Not Invented Here (NIH) Syndrome: a look at the perforomance, tenure and communication patterns of 50 R&D project groups. R&D Management vol. 12, pp. 7-19