She's been pretty forthcoming about the whole thing. She said she wanted a really strong metal and the earth based stores were destroyed so she thought it would be a cool jump off point for the future. She also said it wasn't "Planet Vibranium" just that there was a large reserve of it on that planet.
I'm alright with that response but I'd like to see that firmed up on page at some point so that "the source" is still somewhere out there.
It's that "Pissant Planet where it comes from line" that gets me.