Normally, it makes sense to do this. Negotiate price, avoid hassle of repeated procurement energy, wait until you have more certainty about trial results and manufacturing process.
This situation was a national disaster, not a normal procurement exercise. The EU should have committed earlier to a broader range of vaccines because the cost benefit was trillions of euros of human live and economic damage costs compared to billions of euro of potentially redundant vaccines.
That they didn't do this, and now are scapegoating the manufacturers, is a 'catastophe' from my perspective. Coordination and delays are explanations but not mitigations.