You should have countered that a negative while loop would be even faster! See: JavaScript loop performance - Why is to decrement the iterator toward 0 faster than incrementing.

In while versus for, these two sources document the speed phenomenon pretty well by running various loops in different browsers and comparing the results in milliseconds:
https://blogs.oracle.com/greimer/entry/best_way_to_code_a and:
http://www.stoimen.com/blog/2012/01/24/javascript-performance-for-vs-while/.

Conceptually, a for loop is basically a packaged while loop that is specifically geared towards incrementing or decrementing (progressing over the logic according to some order or some length). For example,

for (let k = 0; k < 20; ++k) {…}

can be sped up by making it a negative while loop:

var k = 20;

while (--k) {…}

and as you can see from the measurements in the links above, the time saved really does add up for very large numbers.