I think most any fish can get ick....
I dont know why some seem to get it easier than others but they do.
Fish go thru alot of stress during collection and transport and shipping and from bagging and different tanks, not eating and sleeping and all that cuases stress. They are scared and confussed and this weakins their immune systems that help them fight off the desease or parisites naturaly.
This seems to effect tangs as well as angels more than others.
Plus putting them in our tanks that have parisites or deceases already present or other fish that pick on them because their new or bad water conditions or wrong food ect. causes decease too.
Im not an expert but thats what I think from what Ive learnd.