I think the reason is just that it isn't widely used. It's a very niche use-case, anyway. Even link-shorteners don't particularly benefit from something like this, and for all cases where the actual amount of data is concerned, simple base64 is more efficient.

But yeah, making a wikipedia entry and adding it to this list (https://en.wikipedia.org/wiki/Binary-to-text_encoding) could spread it a little further.