> You could see that 20 years ago too, unless you manually stored the state of the form somewhere

See, that's my point - it's NOT manual, it's explicit. There's a difference. A form submission and page refresh is just that. It's very clear WHEN the sync happens and WHAT we are syncing.

With a SPA, you throw that all away and you have to do it yourself. And it's almost always done poorly and inconsistently.