Most likely because most people didn’t know you could do that. I didn’t - until now!
It would help if a mismatch was automatically flagged when the genus (or higher) a taxon photo represents becomes void because the taxon (e.g. genus) the species is in changes.
I agree. That would be a good feature request if you’d like to make a new thread requesting that
There already is a feature request about this:
https://forum.inaturalist.org/t/flag-or-otherwise-mark-taxon-photos-whose-cid-doesnt-match-taxon/4556/