Digg didn't fail because it didn't use Java, that's preposterous. Java isn't more scalable, stable or simple than any other solution, that's Java consultancy bullshit.
Twitter would disagree[0].
> We now have the capacity to serve 10x the number of requests per machine. This means we can support the same number of requests with fewer servers, reducing our front-end service costs.
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All phones since the last 30 years (including the famous Nokias) shipped with Java and apps that simply worked. Android is constructed on top of Java. What I build today with pure Java will run in 100 years from today without needing changes. Quite a different scenario for whatever other language that breaks stuff every couple of versions.
Using other languages is of course possible. In the same manner as building a wheel with stone is possible instead of using rubber.
Another pretty extreme view... there are plenty languages that can be used for complex projects.
Anything else is from startups that grew big and simultaneously polarized about their language decisions. Those decisions are tied to whatever lifestyle or political statement, more than a sane engineering decision that addresses technical debt in the future.