The science didn't change.
Even novice virologists know that respiratory viruses, by their nature, evolve quickly and become less controllable by vaccines. Influenza and the common cold have demonstrated this with crystal clarity for decades.
The 'advice' given in the early phases of the pandemic, with their blanket 100% vaccination guarantee, omitted this simple and obvious caveat to vaccine efficiency.
As I said, whether this was malice, incompetence, or both, we won't find out for a few years yet.