Except...And so unnecessary.. They have glass bottles and packaging facilities in the USA, they don't need to transfer the finished product, just tanks of the active soup.
Putting it into packaging that is suitable for delivery to small locations makes far more sense on a global scale. Otherwise you would need soup-to-vial repackaging facilities down to quite small locations. Imagine some relatively isolated place like Tasmania.
One aircraft could deliver all the vaccine they need. (Assuming they can store half of it for 21 days.) But is it sensible to develop a repackaging facility there? I'd say it is pretty obvious, it would be over the top. Just where does it make sense to have repackaging? Sure - the whole USA. But if you have set everything up to deliver vials to most of the world, there is less sense in doing otherwise for one country - however large. And even within the USA, you need vial delivery to many places. So delivering in bulk to a tiny number of repackaging facilities, then forwarding in vials, is quite possibly not worth doing.
Delivering the same form everywhere helps ensure that deliveries can be re-allocated fairly easily.