I don't think it is bugged.
It's a fairly rare badge mainly because lots of tags don't reach 50+ questions on the site these days. I'd say that's primarily due to a few things:
- Game releases and their popularity
- Other sites have answers (Wiki sites as an example)
- Arqade's traffic isn't what it once was
- If you have the badge already, you can't get it again. So if you create a new badge and it reaches 50+ questions, the Taxonomist badge gets awarded to nobody.
You didn't earn the badge because you earned it already back in 2014 for hearthstone and the badge can only be earned once.