On the topic of why managers prefer using IRR over NPV.

I believe the best argument is flawed comprehension. For NPV calculation, we use a discount rate which comes from the WACC or the cost of capital which is demanded by investors. If the rate happens to be high, NPV might come as negative, which immediately concluded as non-profitable. This is wrong, as the Author rightly says; it's not non-profitable, it's just not profitable enough.

In terms of "not profitable" or "not profitable enough" is there a difference in the decision we would make? Aren't we likely to reject either one (and why)?