It should all be down the applications need for client side interactions. Even with hotwire/turboframes, phoenix liveview or other websocket / real time server driven update patterns, it can be suboptimal for many catagories of applications as these rely on (albeit smart) whole replacement of DOM nodes. In heavy applications, or applications that have a lot of represented state, its not the panacea it might seem at first glance.

I always tell people, "mileage may vary, there's no silver bullets in this industry". I think it holds true especially when talking about stuff like this.