In my experience, DMs learn to do this because the players aren't offering much in the way of describing what they try to do, so they are just filling in the vacuum the players create. Then it just becomes a habit for the DM. Players that make a clear statement of goal and approach in a reasonably specific, but succinct way don't leave a lot of room for the DM to do this. If the DM is habituated to this practice though, sometimes even that doesn't matter. And a lot of actual plays have examples doing this, so people pick it up there, too.