The real answer to this, I heard in a Jewish History class given by a Rosh Yeshiva. He said, that Ben-Yehuda, being ashkenazi and coming from a frum background, didn’t want to assosiate the zionist movement with the “old fashioned European Jew”. Taking on the sphardic havara gave Hebrew a new sound, nothing to do with the religious past. It was to wipe away all remenants of yiddishkeit.
