Why can array holes (sparse arrays) behave unexpectedly with iteration methods?

Methods like forEach, map, and filter skip empty slots in sparse arrays entirely rather than treating them as undefined, which can silently produce shorter results than expected. for...of and the spread operator, however, treat holes as undefined.

const arr = [1, , 3];
arr.forEach(x => console.log(x)); // logs 1, 3 (skips the hole)
console.log([...arr]); // [1, undefined, 3]