Maps have a very clear and discrete semantic, no need for a flag or a comment, when someone reads the code if they are not familiar with map(x, things) then they will look it up and quickly become familiar. On the other hand closures say "the rules about variables that you might have thought were the rules are not the rules, these are not the rules you are looking for, move on, move on". People who haven't seen them before will be genuinely puzzled.

Yes, a good programmer will find out what is going on, they will be a better programmer there after. However alot of code is picked up by contractors or off shore, or even just by an intern and what happens then is that they hide their incompetence and introduce lots of bugs, or just fake the tests or lie about the tests.