AT&T’s website account pages only serve static html. But they are rendered by js and I have to wait looking at a loader after every click. Why is that? Why do

AT&T’s website account pages only serve static html. But they are rendered by js and I have to wait looking at a loader after every click. Why is that? Why do so many static websites and blogs use SPA technology for all their pages? It can’t be that it’s just to make me mad (although it works). Are people insane? How does spending 10x the $ and effort for a worse result make sense?