The API between the SPA and the server is an internal implementation detail that doesn’t need to support interoperability or backwards compatibility.
I see no reason to believe interacting with it directly is easier than scraping an HTML page. (In fact, I’d expect it to actually be much harder and more fragile than scraping html in practice)
In my experience scraping both, APIs have tended to be more stable than the structure of HTML pages. I'd guess this is because there's an incentive to keep your API stable (a breaking change for my scraper is also a breaking change for the front-end), whereas there's basically no reason not to rewrite giant chunks of the HTML to accommodate a design change.
I see no reason to believe interacting with it directly is easier than scraping an HTML page. (In fact, I’d expect it to actually be much harder and more fragile than scraping html in practice)