The marketing of "Die Mannschaft" seems a thing for international marketing, since people who don't know the german language won't see any problem with "Die Mannschaft" being wrong in its semantics, they just hear Die Mannschaft when discussing about football, and think about the german national football team.
Seleção literally means "National team" in english and "Selección nacional" in spanish, and it is also wrong in its semantics, because "Seleção" can also be used to refer to other national teams e.g : "Seleção Argentina de Futebol" or "Seleção Inglesa de Futebol"...and brazilian journalists don't give a crap if foreign journalists/fans can't pronounce "Seleção" properly cause they can't speak portuguese.
Die Mannschaft seems like a good nickname, because it sounds very german.
It doesn't need to have an 'esoterical' or 'astral' meaning to make sense, it's all about marketing.
Also, it's actually not a nickname simply invented for marketing purposes. I lived in the US in the early 2000's and people I played football (soccer) with used to ask me about the 'Mannschaft'. I also remember watching ESPN segments in the run-up to the World Cup in Germany where they talked about 'Die Mannschaft'. Obviously, it's a bit weird that the DFB adopted an international nickname as their quasi-official name but at least it's not quite as generic as it's made out to be in this thread.