Why do these Americans like to call themselves expats instead of immigrants?

Like the title said.
Talking about a situation in my city where I met some Americans who keep referring to themselves as expats claiming they are not here for the long run. Keep in mind they live in Germany, do not speak the language but have been around for 10 years.
The idea of making a lot of money and leaving for the US is a bit strange since you earn more money in the US. Both of them also do not speak any German despite living here for almost a third of their life and keep saying the language is too hard.
I am trying to wrap my head around this. My friends from SEA already spoke B1 German before getting here and use the word immigrant and foreigner when referring to themselves.
I have a small sample size but have met a few (5) other who shared the same view on immigration. Interestingly they complain about people not adapting to them since our offices and companies require speaking German.
I do realize that I am biased due to my own experience with Americans but I am curious about understanding the culture behind the though process of immigration of Americans.