However this is not about how many vaccines have been bought, but how many are being delivered via current production. The US, EU, UK, etc have indeed bought more than they needed, but they won't (by definition) be using more than they needed - the extra purchases were due to spreading the production and vaccine approval risk to ensure that enough were available.
You could reasonably argue they shouldn't be vaccinating whole populations, by which I mean including low-risk elements, whilst poorer countries cannot vaccinate even high-risk ones. That's a different question though.
If there is suffering, and if we can, we ease the suffering. The US and EU have bought way more vaccine doses than they need.
It even makes sense from a utilitarian perspective, as we live in a global market economy.
Since when did people become so nationalistic again? We're humans, first and foremost.