Sure, but on modern servers, the amount of data you can put on the stack (or stacks) amounts to no more a few percent of RAM. The smartest thing you can do with the rest, is put as much of your DB data there, and that data has an arbitrary lifetime, and is read -- and written -- concurrently. So most of the memory activity on large servers is going to be on the heap. If you put on the stack everything that can be done on the stack, you've reduced your heap usage by, say, 2%. True, the kind of memory work on the stack and on the heap is very different, but the two problems are of entirely different magnitude and nature.

I think the reason many people say "just use the stack more", is that most people delegate the hard work to a DB, and let the DB engineers worry about using the heap well. But the best way to use a DB is if it is in memory and in process.