Why the "-" in "ex-pat" sometimes?

While "expat" and "expatriate" are commonly used, I also often see "ex-pat" in news articles:

• So You Think You Can Be An Ex-Pat? Forbes
• Australian ex-pat writer and TV critic Clive James dead at 80 Japan Times via Reuters

What is the origin of "-" between "ex" and "pat"?

Note: When I copy/paste this character from the Forbes article into Wikipedia, I am redirected to Hyphen-minus.

Solution 1:

Being the short for expatriate, expat is the correct spelling, without hyphen as suggested in all online dictionaries. Google Books shows few usage instances of the hyphenated form which is a “nonstandard” variant, probably influenced by the usage of the prefix ex- in terms like ex-president, ex-wife etc.

Solution 2:

“Expatriate” is one word. “Ex-patriate” doesn’t work, because the prefix “ex-” with a hyphen carries the meaning of “used to be,” as in “ex-president”, “ex-linebacker”, or “ex-priest”. For the same reason, the colloquial short form “expat” is correct, not “ex-pat”.

Many people misspell “expatriate” as “ex-patriot” (mainly because the pronunciation is near-identical). An ‘ex-patriot’ literally means a former patriot — a potentially costly mistake if used to refer to an expatriate (because it’s potentially defamatory then).

According to Ngram, “expat” seems to be used as far back as the 1800s, whereas “ex-pat” came into use after the 1950s.