Open source is driven by contributions. Most of the time, if someone wants a feature, implements the feature, and submits a reasonable PR to a project, that project will have the feature. In this case, the PR appears to have been written by someone who is not a regular SystemD contributor, and (through a bit of Googling) works for a FinTech company with no obvious interest. I can't comment on why that individual wanted to add support.
However, once someone added support, the question for SystemD is not if it is worth implementing, but if it is worth merging. At this point, it becomes a simple case of "the most intolerant wins". For people who care about complying with CA style laws, this feature is critical. For people who don't care, this feature is fine. I doubt it will even make it on mosts lists of SystemD feature bloat that most people don't care about.
This is the same reason a bunch of the food in your pantry is certified kosher. No one is going to not buy something because it is kosher. But if paying a thousand dollars a year to put a small circle-u symbol on the back of your box can increase sales by 1% among observant Jews, most companies are going to do it.