Gambling on efficacy would not have been a reasonable approach.

I understand the temptation to think that this would be a good way to proceed but developing a complete supply chain for a dud would have been a total disaster for everyone involved and would have taken resources away from viable vaccines.

All of the big vaccine producers had full faith in these candidates and they poured money into their production in advance of phase 3 trials and we are still supply constrained. Making the same bet a month or so earlier (the largest gain possible) would have had a small incremental gain but an enormous downside.