"But among the myriad able, capable, and respectable female politicians in Washington and around the country, why Kamala?"
ol' white joe had boxed himself in by promising he would "select" only a woman "of color" -- that meant "black" -- as running mate.
That pledge right there cut the number of possibilities down to near-zero.
Of course, ol' joe didn't make the final choices -- they were "chosen for him" by his handlers. Even kamala sutra was probably "a hard suggestion" made by the handlers. After all, she's a senator, right...?