"Expatriates" covers the case of someone living temporarily abroad, whereas "immigrants" does not. This site covers many cases that are not "immigrants". For example in the US system short term work visas like H1B, student F visas, company transfer L and exchange visitor J are all non-immigrant visas, and people living in the US under their terms are not called "immigrants" in normal speech. We answer questions about them.
"Expatriates" is not just a politically correct name for immigrants. "Expatriates" as a word has been around for hundreds of years before "political correctness" was even thought of.
It would be weird to expect a user to come to a site called "Immigration" to ask about non-immigrant circumstances.
No it should not be renamed. Or at least not to "Immigration" or anything similar.
However I will say that "Expatriates" is not a common word and may not be understood by people who have English as a second language. It's possible that a change to "Living Abroad" or something similar might be helpful.