SIL

That's wrong. Only the pages of "The Ethnologue" (an historic part of SIL) has a paywall, and there was NO reintroduction

But the part for the ISO 639 registration agency (also hosted in SIL.org) is public (and will remain visible to all, according to ISO policies on this standard), even if it contains also some links to other pages (in The Ethnolog, but also Wikipedia, Glottolog, or the Linguist List, and possibly others). the ISO 639-3 was built initially from an initial setup in The Ethnologue, but then it has been largely reviewed and modified by ISO independantly of The Ethnologue (and various historic codes used in the Ethnologue were rejected in ISO 639-3 and incompatible with BCP 47 as well; later, The Ethnologue was modified to use ISO 639, but not completely as they disagree on some parts of the classification), which is not the exclusive source.

So there's absolutely no reason to block/remove all links in the sil.org domain: SIL cannot decide alone what is part of the international ISO 639 standard and MUST publish everything that is decided by the ISO TC: they are jsut a registration agency and must publish the standard without modifying it, nad must also be open to other external submissions to the ISO standard (including information links and other national standards that could be bound to the ISO 639 standard). And in fact these links to the ISO 639/RA website are NORMATIVE for the ISO 639 standard (other links to Wikipedia, or The Linguist List, or Glottolog, or even to IANA and IETF pages for BCP 47 are NOT, they are only INFORMATIVE about their respective works).