Why do the chasidim originating from Galicia, Silesia, Poland (with the exception of Gur and a few others) use a sefardi knot with the loop outside the bayis instead of the inside as per ashkenazi minhag? Was there a concerted effort to change this or is there another explanation, such as these areas were populated by many sefardi refugees from spain or people who settled there to trade from Turkey?
It is the custom of the Ashkenazi Chasidim who originated in Eastern Europe, to incorporate the customs of the Ari. The Ari famously mixed Ashkenazi minhagim with Sephardi ones, to meet kabbalistic requirements found in kabbalistic literature and teachings (such as the Zohar).
In short, it's the same reason why Chasidim daven Nusach Sfard, a nusach that is not Sephardi, but is Ashkenazi with Sephardi additions to match the teachings of the Ari.
One reason to have the tefillin knot on the outside is so that the strap will be wrapped outward. This is to remind the wearer of the kabbalistic dictum that one must give before receiving.