Just as a data point, as a Canadian I had never heard this name before, and I couldn't possibly name a single other WNBA athlete, whereas I could name international female athletes from many other sports. Here in Toronto, the https://en.wikipedia.org/wiki/X_League_(women%27s_football) (which infamously included a former mayor's niece) is probably better known than the WNBA.
By contrast, the mere words "United States Marine" paint a clear picture of a very particular sort of individual that is instantly legible, internationally.
That may just be a regional thing. I certainly couldn't name a single X league player.
Regardless, she was certainly more famous than some spy whose job required that he not be famous or even memorable. Right choice or not, Biden likely just made the choice that got him the most positive attention, as one does when they're a politician.
By contrast, the mere words "United States Marine" paint a clear picture of a very particular sort of individual that is instantly legible, internationally.