As usual, advocating for personal freedom gets you downvoted. It's such a funny pattern.
But in this case, the answer's very simple, and in my opinion, very obvious: High-risk people value the vaccine more, and allocating a proportion to the open market gives them the option of paying for one instead of having to wait for government permission. This is a first-order effect, not even a second-order effect.
The second-order effect would have been that more people might have been incentivized to create a vaccine if you opened the door for more profits. Right now there are lots of individuals throughout the world who don't have access to a vaccine.
The underlying truth is that a lot of Brits have identified with AZ, and any "attack" to the vaccine feels like a personal attack to their country and their identity to them... You seem to be in that category.
In the meantime, the state has taken a monopoly on the distribution of these vaccines and has even stopped administering them, so while they are available, they are locked away.
I predict for later this year, we will see news reports of batches of vaccines being safely disposed of ( destroyed ).