Symbols that you never use aren't very useful when all you really need to know is "do not dry", "do not bleach", "wash with like colors". It's really not that big of a deal to put a tag written in English and Spanish to the US, or in French to France, etc.
When artists use English, CAD designers use Traditional Chinese, and factory staff use Simplified Chinese or Vietnamese, and consumers use every language - there's a need for a standard symbol. You have a good point about dry cleaning services too!
The difficult part is that the people through this international supply chain can't type these symbols in emails, or search for them in databases. That's why a Unicode code point should be assigned.
This article looks like it has a general summary:
https://sewport.com/tips-on-starting-a-clothing-line-from-43...
This is not her company, but a job description for a similar role (you'll need to translate from Chinese):
https://www.104.com.tw/job/5cuv8?jobsource=jolist_c_relevanc...
I'm with you, it bears uncanny parallels to the PCB design workflow. Not just the Gerbers, but the component/fabric selection, simulation, design drawings, etc.