As a person making what you call "SPAs" since it was possible, first was the minimal amount of data needed to display every next product with use of JS so instant, but then.. rethinked, modularization and being caching friendly (no frames but every replacable part of a page could be as well a page itself - you would call it SPMpA maybe ?) - but the main problem was.. z-index of.. iframes - so you needed to rewrite content elsewhere, with JS, when loaded instead of doing it nicely without it, and finally XMLHttpRequest came from IE - since, any other ways of doing it except with JavaScript are forgotten.
Kind of true the doom came from IE/MS.