I think breaking JS tends to be much more destructive than dead links. At least with dead links there's a fairly clear non-technical fix. With a web standards break, maybe 8 years ago you hired a contractor to build a website that uses a library that uses a library that uses a library that uses some JS feature that is now broken, so your website is now completely broken. Some of those libraries are on older unmaintained versions, where the only upgrade would be through non-trivial breaking changes, or you would need to just find alternate libraries. Getting things working again is a huge undertaking, not just a matter of "don't use that weird JS feature anymore", and I think in that situation it seems reasonable to blame the browser for the breaking change.

It's also maybe more widespread than you'd think. Adding `global` seemed safe for a long time, but ended up breaking both Flickr and Jira because they both use a library that broke: https://github.com/tc39/proposal-global/issues/20