There was certainly no reason to believe, even at the time, that these vaccines would be any more durable over the long term against a rapidly evolving coronavirus than all of the previous attempts to develop such a vaccine. Seems like a lot of people were just hoping that would be the case because of the shiny new tech involved and because they were aggressively sold on the idea the vaccines were the key to "ending the pandemic." Plenty of immunologists at the time predicted that SARS-CoV-2 immune escape would come quickly and that vaccine protection would wear off quickly.