Use it or lose it? Speculation:
Keeping your previous beliefs consistent by rationalizing and distracting yourself are both ways to avoid changing your mind or to avoid thinking about unpleasant things. Maybe most people start with both strategies and the one they have success with develops more than the other. If you are really successful at distracting yourself, maybe rationalization skills never really develop to their full irrational potential.
Anna Salamon and I are confused. Both of us notice ourselves rationalizing on pretty much a daily basis and have to apply techniques like the Litany of Tarski pretty regularly. But in several of our test sessions for teaching rationality, a handful of people report never rationalizing and seem to have little clue what Tarski is for. They don't relate to any examples we give, whether fictitious or actual personal examples from our lives. Some of these people show signs of being rather high-level rationalists overall, although some don't.