I think it depends upon what features a particular framework is offering. I made various POC apps on different technologies, depending upon their promises.
For eg.:
- Newsfeed app using Angular to demo two-way binding concept.
- Polyglot persistence app to prove the use of changefeed in RethinkDB.
- Super fast web server to handle more 10K/sec request using Node.js to prove it's I/O handling.
- Google-like search engine to demo ElasticSearch use.
And list goes on and on...