The problem with those tags is the risk that their selection and application has the risk to become really wanky. Like say, do gender or race-swapped characters still get the "POC" or "female" character tag, or is not not really highlighting female and POC characters if the art is about a popular (usually) white male character? Should there also be "non-binary" tags? do aliens with different genders count for any of those? Do green or blue characters count as POC if the actor is a POC in RL?
ETA: Those issues aren't necessarily a reason not to have these as extra tags, they are just less simple categories than fandoms, and the possible disagreements over how they should be applied are more contested (and potentially hurtful) than fandom tags, because "gender" as well as "whiteness" (to which POC is usually constructed in opposition) are very fraught categories, and subject to change too. Like another problem with a POC tag would be whether for example in historical period fandoms characters that at that time were excluded from counting as "white" should "count" or not because today they are mostly considered "white"; or what about characters that could "pass" but identify as POC culturally? What about Latin@ characters? Latin@ characters are definitely underrepresented in US media, but can considered white or not in an US context depending on ancestry, and other countries have their own historically grown systems of (degrees) of privilege that correlate with skin tone, ethnicity (and other things). Count all otherwise "unmarked" manga characters from Japan as "POC" because there the "default" is Japanese, which would be a POC in an US context, or don't they count because they aren't "minority" characters and the tag is supposed to encourage representation?
Re: More tags
ETA: Those issues aren't necessarily a reason not to have these as extra tags, they are just less simple categories than fandoms, and the possible disagreements over how they should be applied are more contested (and potentially hurtful) than fandom tags, because "gender" as well as "whiteness" (to which POC is usually constructed in opposition) are very fraught categories, and subject to change too. Like another problem with a POC tag would be whether for example in historical period fandoms characters that at that time were excluded from counting as "white" should "count" or not because today they are mostly considered "white"; or what about characters that could "pass" but identify as POC culturally? What about Latin@ characters? Latin@ characters are definitely underrepresented in US media, but can considered white or not in an US context depending on ancestry, and other countries have their own historically grown systems of (degrees) of privilege that correlate with skin tone, ethnicity (and other things). Count all otherwise "unmarked" manga characters from Japan as "POC" because there the "default" is Japanese, which would be a POC in an US context, or don't they count because they aren't "minority" characters and the tag is supposed to encourage representation?