It's the same reason companies with tiny apps in the cloud default to kubernetes even though it could have been done with something simpler like AWS lambda.
Consider that backbone.js was developed by Jeremy Ashkenas to solve problems the NYT had with its layout. Perhaps the problems they have are more complex than what you suspect?
I believe React/Vue will ultimately be replaced by recent modern developments using websockets to trigger the delivery of server side static async views. This is how Github/Shopify now does it, ala Elixir's LiveView, and Rails itself also has ActionCable+Turbo/Hotwire. It is far superior as it keeps logic in one place in the backend and in one language. But that is far from mainstream yet like React is and there will always be legacy features that need to be supported.
But hopefully it will become the standard and JS will limited to necessity.
For ex: some components on pages like charts/graphs, multi select boxes with autocomplete, etc will still require JS that websocket/ajax triggered views can't replace. But those are easier to package into standard libraries. Whether reactive vDOM will still be needed for that idk.