Flags are not always seen by curators because there is currently no way for a taxon curator (or anyone else) to be automatically notified of a flag on a taxon. It’s something that has to be actively monitored.
Personally, as a taxon curator, I wouldn’t mind getting an @-mention to draw attention to a flag in the taxa I curate, but it’s possible other taxon curators would prefer that you wait until they have time to get to it.
Taxon flag notifications have been requested, and are definitely on the list of ways to make taxon curation easier. Hopefully in the notification update to come, this will be possible.