I don't think the benefits of charging for your work are mysterious. It's reasonable to believe that certain works should not be behind paywalls, but not understanding is kind of a confusing stance.
Well, for ISO it is a business model. And for a lot of standards which have limited interest in a certain industry and you are probably going to spend $2000 on gear to make measurements compatible with the standard it is not so bad to spend 133 CHF on something.
On the other hand I served on a committee and wrote a technical report that costs 133 CHF and personally I'm a bit annoyed that (1) I can't send you a link to read it for free and (2) a friend of mine who worked for the US government and is the only person I ever met who knew how to do complex modelling in OWL couldn't contribute her writing to it because everything US government employees write is supposed to be public domain.
If your entire goal is to create a standard... it seems like giving anyone access to the materials needed to _adhere_ to said standard is prerequisite.
Unless the goal is not to create standards, but instead to control access to said standard.
As someone working in standardization: I don't know any standardization organization where the people doing the actual work of writing standards are paid for their work. I certainly am not.
In the organizations I know - including ISO - the money is basically exclusively spent on "overhead".
There was a time when buying the Ansi C standard cost over $200 but you could get Herb Schildt’s “Annotated Ansi C Standard” for $20, which some said reflected the value he added to the process.