It’s not the default, which may play a big part. In addition, justification is an awful way to align text[1], making the composition uglier and harder to read, even if you don’t consciously notice it.

There are ways to work around those issues (all of them hacks: deforming characters and spaces in between), but even most professional design software doesn’t support the full range of features. Last I checked, Adobe Illustrator didn’t support that kind of granularity (though Adobe Indesign did) and neither did web browsers.

[1]: https://en.wikipedia.org/wiki/Typographic_alignment#Problems...