I agree that it doesn't matter what value of n you specify for dbcache=n, even when I don't exactly know how Bitcoin Core actually allocates memory for such caches.

But 4 KiB pages aren't the only size that most CPU and OS architectures support. There's usually also something called large or huge pages, because having to manage only a fixed small size like 4 KiB isn't efficient in certain cases.

Maybe have a look here to dig deeper, for those who are interested: https://en.wikipedia.org/wiki/Page_(computer_memory)