There's no reason to use two languages. All the major server-side frameworks still exist and many have been upgraded with the modern component style templating

There's no reason to use two languages. All the major server-side frameworks still exist and many have been upgraded with the modern component style templating for the frontend too. Nothing is new with JS frameworks. Hydration and fancy "resumable" state has been done over a decade ago with serialized viewstate and AJAX controls. The JS world is just discovering how powerful server-side stuff can be after all this time.