@alcinnz i suppose the problem it solves is, if the html “document” actually represents the UI of some kind of application, it’s a bad experience to require a full page refresh for every meaningful interaction, especially form validation. forms are especially complicated for screen reader accessibility as well.
@alcinnz in the less extreme case, it kind of sucks to need to listen to all the menu options over and over again on every page navigation. thankfully most screen readers are smart enough to let you skip it, so long as the page is marked up correctly and includes a “skip to content” link.