I guess if I had to say a reason I just don't believe you can create a solution this quick unless you created the virus.
The reason you think that is because you're basing it on old science.
In the old days (and by old days I mean about 30 years ago) you couldn't really make a vaccine until you found a ground zero cause. Once you found that, you could formulate a vaccine.
That's what took the longest part of it all: finding the actual source. To wit: we've still not positively identified the origin of Covid 19. Were we still using old science, we still wouldn't have a vaccine to this day.
But luckily, we're not using old science for this. We're using new science.
The Pfizer and other vaccines are based off of synthetic messenger RNA. When you're using that, you don't need the ground zero cause. All you need is the virus itself, which we had PLENTY of.
You break that virus down into its genetic code and use synthetic messenger RNA and code it to tell the human body how to react to the virus in question.
It's hot stuff, man. It really and truly is.
That's how it happened so fast: all scientist had to do was decode the virus they already had and formulate a synthetic RNA messenger to tell us how to beat it. We didn't need the antibodies of the ground zero subject like the old technology was based on.
So if you ever watched the movie "Outbreak" and think that's the way we do it, it's not. That's old school technology and frankly the movie is full of shit. Even after they found that monkey it would have taken months if not years to formulate the vaccine.
Synthetic Messenger RNA is next level stuff. That's how it happened so fast.