I agree that the observer’s choice of the focus of the observation has priority and IDers need to respect that.
However, in cases where the observer entered the observation with no ID and no notes about which organism they were interested in, identifiers have to make their best guess. Inevitably, sometimes they will guess wrong (none of us are mindreaders and sometimes the organism of interest is not the obvious focus of the observation). So the observer also has some responsibility to make this clear from the beginning.
When the observer fails to indicate their preference until the observation has multiple IDs, it may be the more pragmatic choice to duplicate the observation rather than try to get all previous IDers to withdraw or change their IDs. Some IDers may have unfollowed the observation or they may miss notifications – and they have already put effort into IDing the observation. Asking them to come back and change IDs that were made in good faith also seems somewhat inconsiderate of their time and energy.