We chose React.js because of its overwhelming popularity among developers in addition to the fact that its programming paradigm can be used for both web and native app (when coupled with react-native).
We chose DigitalOcean as it is the only hosting provider that also has a Platform-as-a-service software like App Platform. That way, our dev team can focus on creating value for our users instead of spending time managing infrastructure.
We chose github + github actions in order to manage the code versioning and the CI on the same software. Furthermore, while it is not that much, I believe that for a large team it is considerably cheaper to have one github subscription instead of a git subscription and a CI/CD software subscription.
We chose to use JavaScript/TypeScript in both frontend and backend in order to reduce the developer "friction" when working full-stack. I also believe it helps when teaching junior developers the ropes of the work.
NestJS has a very good documention. Furthermore, as a former django-user myself, I believe it is nice to finally get a backend node.js framework very much opiniated like Django. It may be related to what I previously said, but in terms of enterprise-used framework, it seems that Nest.js is the most popular.