Nope; if Lisp were popular, all the fungible programmers would readily learn it and be productively employed, just like the are currently doing with languages that borrow heavily from Lisp.
Employers don't actually want fungible programmers, as in mediocre. They want programmers who are replaceable not because their work is mediocre, but because their work is well-designed and organized with a view toward maintainability, documented, and covered by test cases.
One can easily be a mediocre programmer (who therefore ought to be fungible, because their work isn't clever) but whose work is difficult to understand, take over, and get working by the next mediocre programmer.
Employers don't actually want fungible programmers, as in mediocre. They want programmers who are replaceable not because their work is mediocre, but because their work is well-designed and organized with a view toward maintainability, documented, and covered by test cases.
One can easily be a mediocre programmer (who therefore ought to be fungible, because their work isn't clever) but whose work is difficult to understand, take over, and get working by the next mediocre programmer.