Sure they don't, but saying that you are going to force logically separate pages onto a single page is starting from a point of bad UX and trying to dig yourself out of it.
In theory, the only irreducible UX distinction surrounding logically separate pages in a traditional website vs a SPA is that the SPA doesn't do the full postback, which is arguably a better UX.
Sure, in practice many SPAs might be subpar, but then the debate shifts to "are SPAs are difficult to implement correctly," rather than "SPAs for blogging engines (necessarily) creates horrendous UX". There are existence proofs of well-designed SPAs with logically separate pages and excellent UX.
As an aside, someone who pattern matches on "SPA = horrendous UX" might not even notice a well-designed SPA, further entrenching their belief that SPAs are a Bad Idea from a UX perspective!
SPAs for situations where they are not needed are horrendous UX in and of themselves due to the usability issues for power users that manage JS execution via browser plugins. [e.g. uBlock]
Fair enough, but I think that's a separate issue. If we go down this path, we'd be diluting the term "UX" to homeopathic levels. I wouldn't criticize an iOS-only app for bad UX because it ignores half the market.