I understand your point of view. But in practice, if you check how both words are used in practice, it is not a permanent or temporary movement that is used to distinguish them. As I commented elsewhere, if temporary fruit pickers that move to other country were labelled "expats" I would fully agree with you. But they are not, which indicates regardless of the self-view of some immigrants (temporary or permanent) like, perhaps, yourself, in practice the term expat is used to label "desirable immigrants" and immigrant for "undesirable immigrants", I just think that if a single term was used, people would be forced to see the immigration issue from every point of view instead of pick and choose.