Design Patterns: 1994 [1]
Java: 1995 [2]
Scala: 2003 [3]
Clojure: 2007 [4]
Unless these hypothetical developers of yours are time travellers, your proposed solution wasn't an option for more than half of Java's life. Sometimes Java is 90% of what you need and you just get on with the other 10% because the alternative (learning a new language, finding a new team or training an existing team to use it correctly, etc.) is simply not worth it to anybody with real world time/quality/scope constraints.
[1] http://en.wikipedia.org/wiki/Design_Patterns
[2] http://en.wikipedia.org/wiki/Java_(programming_language)
[3] http://en.wikipedia.org/wiki/Scala_(programming_language)