Bureaucracy, and scarcity. Personal freedom to buy it would be great if there were more than plenty for everyone, but right now they should be given to those who have a much higher risk of severe complications and/or death. Not even the US allows private selling right now.
When dealing with complex dynamical systems (such as markets), you don't get exact answers. You get general phenomena which require intelligence to understand.
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.
So the fact that the EU will not renew a contract at expiration in favour of other providers is impacting your freedom?
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.
You must be delusional. What's preventing you from being vaccinated is the scarcity of vaccines, and those being allocated to the people that need them most, instead of those that pay the most. If they were sold on the free market the price would rise rapidly above the current price, as demand outnumbers supply by at least an order of magnitude.
Western 'Free markets' are not free at all, and the sale of these vaccines could be regulated to a fixed price.
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 ).