I feel having to go into the game with what was effectively a third string bowling attack was the key factor, which combined with poor shot selection for most of the batsmen made winning impossible.
Ed Pollock was the only batsman that looked comfortable and able to score at the pace required.
Very good report on the game by David Hopps for Cricinfo
https://www.espncricinfo.com/series/vitality-blast-2021-1250122/worcestershire-vs-birmingham-bears-north-group-1250341/match-report