Picture several thousand lines of C++ being reduced to 27 lines of Clojure and you get an idea.
That's not to say that you couldn't do something similar in C++, but I've met like 4 really really good C++ programmers in about 15 years of programming, so no, it's unlikely to happen.
Higher-order functions. It's like the difference between calculus and arithmetic. If you're adding numbers together you're not going to see much difference. If you try to send a man to the moon... it's going to be a lot less code in a higher level language.
Imagine merging thousands or millions of records into disparate timelines by various attributes, merging similar records, or overwriting, changing lengths...
This is the sort of stuff that filter/map/reduce is really really good at, but also, it can be important code that people will pay you a lot of money to write over a longer period of time....
That's not to say that you couldn't do something similar in C++, but I've met like 4 really really good C++ programmers in about 15 years of programming, so no, it's unlikely to happen.