Was that because you now structure you code in a better way, or was it because of React's functionality? And what aspect of the functionality was the most productive? The templating system? Did you used to hand-code your HTML in jQuery, or did you use templates in the HTML document?
A bit of both. With React we now have a much nicer code structure, because it forces us to think in components. We have a JS file and an SCSS file for each component. Before we rendered the view on the server side with Python/Jinja2.
I think there are many reasons for the productivity boost. Thinking in components, more readable code, great debugging possibilities, understandable data flow, to name a few.
We use React since four months, and we develop faster compared to before, when we used only jQuery.