Why is only the last element kept in the array when iterating over an array in js?

Question

underscore.js

jsfiddle.net/arg6gcxk - why is only the last element left in the subarray when populating a multidimensional array?
In each subarray cow, fish, flowers - only the last header is preserved, and it is necessary that all elements of the subarray be in the arrays cow, fihs and flowers

Answer 1

And if so?
jsfiddle.net/2tLLkrLL