It also doesn't bother me much on here because HN is much faster than these systems - no wonder, since it's just a forum. But try updating the details of 50 employees, each separated into 5 subpages, when you need to wait 750ms to have each page load. And you need to load that page multiple times - first to get into the detail, then to put it into "edit" mode, then to save it - and then you can switch to a different subpage of the detail.
Wait, what? If it's taking most of a second for a page to load, then that's the problem, not that it isn't a SPA.
Using the phone that's very annoying. I have to long press on the entry's link on the header, open in a new tab, recheck the message trail, and go back to the first tab to end writing.
So simoly as that, I could think of lots of times where a SPA-style dropdown editor box inserted in the conversation view, would be more useful than the current HN's reply page.
If the reply page contained the whole discussion, though, the problem would be equally solved too. So I'm not saying that an SPA would be 100% better, just mentioning an example that occurred to me.
And yet here you are, using HackerNews just about every day, which works exactly the same way. No SPA. No 'forever loading', just a classic, fast SSR webapp that treats individual pieces of content as documents, just like how the web was designed to work.