why is there no Tenshi (catfish) tag yet animalization tags for every other well known touhou animalization, it makes absolutely no sense
Probably because it's from a niche spinoff fighting game of a niche vertical shooter series that released five years ago and was only ported to consoles more than a year ago. There's only three examples of catfish Tenshi on Danbooru, so it doesn't strike me as all that "well known".
You could just make the tag yourself instead of complaining that no one bothered to make a tag for something that barely exists.