Why does salt make boiling water cook food faster?

Salt does not actually make water cook food faster by any meaningful amount. The common claim is that salt raises the boiling point of water, which is technically true, but the effect is negligible with typical cooking amounts. To raise the boiling point by just one degree Celsius, you would need an enormous amount of salt, far more than anyone adds to a pot. Food cooks faster in salted water primarily because of flavor and osmosis, not temperature. The real reason chefs salt pasta water is taste. If there is any minor speed benefit, it comes from the slightly higher boiling point, but it is so small as to be practically irrelevant. Salt is about seasoning, not cooking speed.