Because they aren't 'available'. The EU is currently at just 15% vaccinated. Stopping the use of some vaccines means it will take longer and longer to vaccinate

Because they aren't 'available'. The EU is currently at just 15% vaccinated. Stopping the use of some vaccines means it will take longer and longer to vaccinate people during which time more people will die, not to even speak of the other negative effects of the prolonged pandemic.