- You need to purchase multiple standards (at least 4).
- In theory, you need to purchase a multi-user license if more than one person should be allowed to read the pdf in your company (hint: nobody purchases the multi-user license).
- Every few years, new versions of the standards are released which you have to purchase.
- Sometimes, you just purchase standards to realise that they're not applicable to your company.
- The industry is riddled with shadiness: A German standards web shop offers a "standards flatrate" for a "great price" of e.g. 750 EUR for 10 standards. 
- Getting off-topic, but more related shadiness: Your purchased PDFs are watermarked with your company name and full name of purchaser (!) in the footer of each page to prevent sharing.
And in case of standards in computing, like ISO 8601 - a lot of them are of interest to open source developers. If they could access them for free, they could make their code compliant. Software companies use a lot of open source, and often whether or not a product follows some standard somewhere is entirely dependent on whether the OSS component it uses follows the standard.
How does the law treat this differently from a book? You can buy a book and then give or sell it to whomever you wish without any restrictions... how is this different?
Then there's also another side to digital distribution, especially in entertainment — if you bought a (heavily DRM'ed) video game, or a movie, or a book, or something else, online, it's tied to your account. You can't lend whatever it is you bought to a friend like you absolutely could the same exact thing on a physical medium. You can't resell it either. You also rely on the mercy of the seller to not pull your access to the thing. Yet, even though it lacks this basic trait of a physical medium, sellers treat digital and physical as mostly the same thing.