Before 2020 the concept "national lockdown in response to a virus outbreak" simply did not exist. There were no consensus in the scientific world that a lockdown would be an effective measure to improve peoples health, all things considered.
If anything I think the Swedish weak response was an effect of listening too much to expert opinions and politicians not taking initiatives and making their own judgements.
Early in the pandemic there were many predictions made on number of deaths etc by some scientists. These models often overestimated the number of deaths/cases. Science is important but it's messy and it takes time.