Because those esoteric languages are better. The comment I responded to points out that TFA makes the unreasonable assumption that the Java programmers and the Smalltalk programmers are equally talented. And that perhaps what is going on is that the people attracted to explore beyond Java are more curious and perhaps more interested in their craft. If that is the case, then I predict these people will be better in Java, even if it isn't their first choice.
For one thing, highly popular languages tend to have communities which are flooded by people who can't use those languages, can't describe the problems they are solving, or can't understand basic programming concepts.
Like, it wouldn't even matter to me if PHP is a good language if I have to sift through thousands of comments of "I did this and it worked" without any description of why it worked, why it is better than other ideas, or what problem it is even meant to solve.