Because they spent the money to develop it and they own it and they are a for-profit corporation.
I didn't say it was the choice I personally would make if I was the owner of the company. I would choose to make it available if I had the ability to. But based on the historical decisions made by pharmaceutical companies in valuing private profits more than world health, I would not be surprised if they chose not to. Frankly, I'd be more surprised if they did.
I just took umbrage in your "we" like it was a decision that we as a country or entity had any part of. It isn't owned by any "we" that I am a part of or "the global poor" like these companies could just hand over the formula for these vaccines to groups of poor people on the streets of a third world nation or something.
It was worded as a philosophical question seeking real world answers. Sure "we" would.