They probably believed, or were led to believe, that being vaccinated meant they could live their lives without masks or restrictions. That certainly has been proven to be a lie.
It is no lie that they said once fully vaccinated you could live without wearing the mask. The Delta Variant had not existed when that was said. Now we have the Delta Variant. You could be vaccinated, but you also could be a spreader in the indoor situation due to its contagious nature. More people could have got vaccinated to stop this situation.