Henrik, it has nothing to do with physical attraction. Neither Gingold nor Hamilton--nor, really, Regina Resnik or Zoe Caldwell, other actresses who have done well by the part--were exceedingly beautiful. But the understood the character, her ethos, her life choices. Stritch, Lansbury--and, purely on conjecture, Arthur--didn't or don't come off that way. She's not salt of the earth, she's not eccentric, she's not relatable. Sure, the fact that even as a young woman Bea looked like a GI doesn't help, but her attitude and performance style alone seem so wrong for Madame A.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body