Fish sauce is a salt and enzyme cocktail. Besides the enzymes from the fish itself, there are enzymes added in production to ease things like descaling, skin removal / breakdown, etc.
These enzymes will continue to be functional and will act on the steak (or whatever) until they are denatured during the cooking process.
Not unlike the step-cooking of 103F, then 120F to "warm age" a steak for tenderness with it's own natural enzymes before the final cooking step.
I've tried a lot of "dry aging substitutes" or shortcuts over the years, salting, koji rice, warm aging, controlled fermentation, etc... Some yield better results than others, but never really found one that comes close to true dry aging.