The upside is that you can link just about anything in GitHub, and those links work consistently and point at the exact right content. This is much less common with SPAs.
I agree its a valid criticism of parts of the ecosystem, but a lot of people these days are using next.js, nuxt.js or sveltkit and those give you easy patterns to follow so that all those things work, basically for free. SPAs are better now than they were just a few years ago.