Alexander ripped them to pieces. If they were great, that just makes his feat all the more impressive.
Another obvious reason to build 'em up is to emphasize the accomplishments of pre-Islamic Persia; the reason this gets a free pass from the worldwide wanker society is that it appears to be pro-Iranian propaganda. It will be used that way. It should be interesting to see what that does to that rickety alliance which supports Greek analogue to Anschluss on Cyprus and the islands of the Aegean.