why the GR"A wanted to leave Vilna and journey to Eretz Yisrael

You find in hil aveilus, perhaps more than any other area of halacha, minhag piled on top of minhag.  R' Moshe Tzuriel in the end of vol 2 of his Otzros haTorah collects a list of practices that people are makpid on that are in fact problematic mi'dina or have no basis, as well as practices that are binding mi'dina but people neglect.  Even if you are not interested in hil aveilus per se, he opens the section with a general discussion about conflict between minhag and din.  He quotes a fascinating tidbit from R' Yaakov Kanaha (son in law of the GR"A's brother): why did the GR"A dream of making aliyah given that the Torah centers of the world were in Europe and Eretz Yisrael was still pretty much barren?  It is permissible to leave Eretz Yisrael to learn Torah, kal v'chomer one need not leave chu"l if doing so would entail bitul Torah?  R' Yaakov Kahana answers that the GR"A was so disturbed by the minhagim that had developed in the European communities that he felt it was worth the journey to E"Y to escape and start with a clean slate in a new community!