This is indeed an issue but it's widespread and everyone does it, including Google. Things like servers no longer generating actual dynamic HTML, replaced with servers simply serving pure data like JSON and expecting the client to render it into the DOM. It's not just Google that doesn't care, but the majority of web developers also don't care.
There's clearly advantages to writing a web app as an SPA, otherwise web devs wouldn't do it. The idea that web devs "don't care" (about what exactly?) really doesn't make any sense.
Moving interactions to JSON in many cases is just a better experience. If you click a Like button on Facebook, which is the better outcome: To see a little animation where the button updates, or for the page to reload with a flash of white, throw away the comment you were part-way through writing, and then scroll you back to the top of the page?
There's a reason XMLHttpRequest took the world by storm. More than that, jQuery is still used on more than 80% of websites due in large part to its legacy of making this process easier and cross-browser.
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