Soda crackers have been a standard size for years.  They were made from a dense kind of yeast in the past, because they were a staple food that soldiers and hunters could take with them in pack packs; and eat for long periods of time, without the cracker becoming stale or moldy.    As the modern age arrived, and food were being mass produced, and were covered with plastic, for freshness; changes were made to the yeast agent and to the baking powder.  This was done to make the crackers light and crispy without losing their shelf life and good taste.  The yeast used today has a fast acting ingredient that adds to the flakiness and makes the cracker taste good. However, the cracker still retains its freshness without being hard to chew.  The crackers from previous decades were hard, which is where the term “hard tact” comes from.  Those crackers were often dipped into soups that were made on the camp fires, out in the wilderness.  Over all these years, the size has stayed standard.  The only difference in appearance is that the puncture holes, that help the flour rise, were larger back in the day.  Since they are part of our history, this is probably why crackers remain popular and unchanged in size.