Like why haven't achievements for meowscarada and metagross and gyradose been added yet?

Seems like there has been plenty of time snd for achievement hunters like myself its kinda upsetting I bought all 3 of them on release in hopes of having their achievements to look forward to doing/getting them and nothing for awhile now?

Just wondering why they haven't been added as quickly as others and or of we have an idea when they will be added or an answer as to why they haven't yet.