From what I've heard, a large chunk of the issue is internet cafe culture in the East, and how they generally are charged by the hour. This leads games to try to aim for average game times that are factors of an hour, so that those who frequent such locations are able to play a few games, and leave contented, and not feeling like they wasted their money on time they cannot use, or had to pay for another hour, just to finish another 5-10 minutes of gameplay.
As a result, some game developers are striving for either 15, 20, or 30 minute average game times, so that such gamers may play 4, 3, or 2 of them per hour they pay for. Of course, with lobby/queue times, and loading times as well, game developers actually have an incentive to undershoot these time targets, and minimize the amount of time these features take up, even at the cost of gameplay or clarity. Take for example, DYNAMIC QUEUE or AUTOFILL or how they changed the way you re-enter pre-made lobbies, and 'play again.'