Maybe it’s nothing at all.
Maybe it’s publicly known (I couldn’t find it).
Maybe it’s a case of covering up acting class oligarchies.
To see these two people acting; their physical similarity (they practically look like clones of each other), personality, facial expressions, vocalizations, timbre – these similarities are astounding to me.
Two that look alike and SOUND remarkably alike: Sherry Stringfield (Dr. Susan Lewis on ER) and Peri Gilpin (Roz on Frasier.) They look more alike in person than the still photos suggest. But not related.
Of course, you also have Natalie Portman and Keira Knightley, who are so close that the latter has played the former’s decoy.