Some reasons: * Nobody required this from them before. * Recursion is rarely used to write business logic, most common thing programmers write and learn. Same

Some reasons: * Nobody required this from them before. * Recursion is rarely used to write business logic, most common thing programmers write and learn. Same for static methods and being generic. * Type checking is done by compiler for them, so no surprise that they don't know how to do it. * Relatively few people go beyond minimal, so adoption of is java 8 is low Overall, it looks like a good question to pick up the best developers - assuming this is what you want.