1. Adaptive design: it’s easier to adjust user experience to the client device capabilities. SPA frameworks take the job of ensuring browser compatibility, but it’s not just it.
2. Less traffic in data-rich apps (even taking into account compression, HTML is heavier than JSON and not just due to syntax overhead - consider all those page headers, footers and other common parts).
3. Better UX for slow networks: even in countries with 5G coverage there are still a lot of corners where your device will struggle to connect. SPA can auto-retry, just showing the spinning wheel longer. Browser will show the timeout page, and who knows if the backend can correctly recover on refresh.