These are very good potential explanations. Also, as with most evolutionary/biological "phenomena" it is important to consider the possibility that the trait under consideration wasn't selected for but is simply a consequence of other traits (i.e., a
spandrel). Thus, lack of belief revision may simply be a consequence of having a general learning system because, say, "initial" impressions must have a larger effect than subsequent impressions due to the general dictates of the system and/or the spectrum of biological possibility.