I agree that the view layer has not been Rail's strength. It's largely handlebars era inspired and has never really changed.
In some ways I think rails never really needed to change because the view layer worked without issues. I always felt the solutions in the modern html/javascript world were messy and half baked, with many unforeseen tradeoffs and complexity for the benefits you get (this summarizes my experience with the whole SPA era).
We are only now starting to have best practices and reasonable design around how the html/js view layer should be done. But I think many people in Rails will continue to prefer the old way of views just because of the simplicity of it.
You'd be surprised how such a small library like turbolinks has held off the entire wave of webpack / react / SPA.