Because writing extensive papers analyzing current and past international politics is easier than calculating dipole moments and memorizing cell signaling pathways? This has been said before, but you can't make comparisons like this. The generalizations just don't hold up.
So these were upper level psychology courses then? You know, the kind that make up the majority of the study a psych major pursues? Regardless of your experience, we all know that generalizing based on anecdotes is logically unsound. In any case, I wouldn't be surprised if many times attitudes like these stem from cases where a student takes an intro course (general psychology or the equivalent from X department) and assumes because it was easy that the whole major is easy. Adding to that may be the perception that students in X department (where the intro course was easy) seem to do well, though one would do well to remember that there is likely self-selection going on here. Students that do well in a particular course of study likely chose it out of intrinsic interest and motivation to pursue the material, which would contribute to their success.
Are some majors easier than others at any given school? Probably (though there may be exceptions for very rigorous schools.) Are any majors unequivocally easier than others for everyone at every school? There is no way to confidently make such a claim.
. But I just remember that I am following my passion and nothing that they can say will defer me from becoming a health professional. 
