In general, /h/ and similar sounds are quite frequent in semitic languages, in Hebrew it even forms the definite article. So, speakers of semitic origin would seem to me more likely to pronounce the aspirations even when they were no longer pronounced in other dialects, at least except for very formal speeches imitating Classical Greek. As Greek was widely spoken also in regions where important part of the population had a semitic native language, I would expect the dialects spoken there to retain the aspiration longer than the dialects spoken in Greece.
Is there any evidence for or against this theory? Or hints at least?