It seems like a vastly inefficient method, purposefully designed to make it difficult for waiters and unsatisfactory for customers.Here, most people drink soda (soft drinks) with their meals, so if you drink what's in your glass your server has to take it back and fill it up again (some places just bring you another glass, or refill you from a pitcher.) But generally speaking, you can't get your own refill at a casual dining restaurant.
It is customary for refills of soda, tea, or coffee to be free.
Well, I think a big part of it is that the soda and often lemonades they bring you don't come from bottles or pitchers, they are from the soda fountain machines (I can't think of the proper name for them so here's a picture: Soda thing). And refills are free; I rarely need a refill, but most people drink at least two glasses, sometimes many more when they eat out. So, the server fills up glasses using the machine, brings them to the table, then when they are getting low brings out another round from the machine, sometimes clearing away the old glass and sometimes just leaving it there to be cleared away with the rest of the dishes at the end of the meal. The machine is hidden away in the back area so that customers can't get the refills themselves. Beer, wine, and other alcoholic drinks, as well as specialty drinks like milkshakes, often do not have free refills and you would need to let the server know you'd like to buy another one.
Based on all this, customers here have come to expect that before your first drink is empty, the server will have remembered which drinks everyone ordered and automatically bring you a refill; you shouldn't have to ask for one.