The problem is that this option is to buy AZ's current vaccine that have a high probability of being ineffective in 18 months. EU is not saying that it won't buy from AZ, but as of now it's not well spent money to buy their current one to be delivered in 18 months. By then all companies will have new better vaccines and the EU would have to fork up a shitload of money on the new AZ vaccine and just write the old of as another loss while the AZ execs get another fat bonus paid by the EU citizens.