How/why?
Well, they were at the forefront of the digital trading card scene, predated only by Spells of Genesis and a handful of Rare Pepes. This makes them of interest to the vintage token / historical NFT community, which I suspect will grow along with the success of dissemination of Bitcoin.
https://cointelegraph.com/news/bitcoin-rebranding-in-japan-bitgirls-tv-show-to-sugarcoat-mtgox-drama
According to this article, the BitGirls series on Counterparty has the following distinctions:
First (and only?) NFT related to a TV show / mass media
First NFT with interactive voting system
First NFT with only women
It’s on the golden era of the history of NFT, when only a few NFT project was live. You know how crypto is moving fast, and this project is from 2016, more than 5 years ago.
Here's an example of one:
And this is its entry on the xchain block explorer:
https://xchain.io/asset/CHIKARINBG
For more info, check here:
https://rarejapanesenfts.com/collection/bitgirls/