It's about targeting contribution and letting potential contributors know what we're using so that they can know and self-select.
Goal #1 of the site currently is recruiting contributors b/c we aren't at a 1.0 release yet. We have it running in several hospitals in the charitable network that I serve, but it's not ready for wider distribution yet.
We want to get there by July 2016. Once we get there, we'll refocus the purpose of the homepage.
I've seen situations in real life where someone will say "hey this tool is cool, how did they make it?" and another person "oh they used framework X, I think." A good chunk of people will then do their due diligence and discover that it was Framework Y not Framework X... but not everyone.
There are some people still to this day, for example, who believe that AngularJS powers Youtube's desktop site.
You're likely recalling the recent article on HN that showed Ember taking longer to download the first time vs. React on a mobile phone.
In a third-world offline hospital records app, the first time difference isn't especially important, and also it's more likely the hospital record keepers will use tablets, not phones.
They're currently working on a way to get past this, by actually enabling server-rendering (much like react):