Well, for starters, can you imagine a Russian or Chinese person saying “Pontiac” — just the word itself? They’ve never even heard of it — so take up would be very difficult.
Secondly, it would be extremely expensive to launch a new brand in markets that are new to it. That’s why Opel, having a global presence except for that in North America, has a much better chance of being “globalized” — it already exists (or will exist this year) in most of the world and is also respected in most of the markets in which it is sold. It would cost a tremendous amount less to bring Opel to NA than it would to 1) bring back Pontiac in NA and then 2) make it global.
On top of that, how and where would Pontiac be positioned in über-competitiev markets like Europe?