As you can see, across all regions, in every elo, the average game time is below 30 minutes. The game in its current state is just too snowbally. Now, what might have caused this to happen? I believe it has something to do with how weak towers are. More often than not, the team that gets first tower is the team that wins the game. This wouldn't be such a problem if towers weren't so easy to kill. If you recall and let the enemy laner(s) push up the lane, by the time you get back to lane(unless you have TP), your tower is already half-health, almost dead, or dead. Towers also provide no protection at all once you are set behind. The enemy can freely dive you after 6 and there is nothing you can do about it because towers do the equivalent of a tickle to tanks and an ADC with 15 shields. Once one tower dies, the rest fall like dominoes, and before you know it, the nexus is dead or you already ff'ed at 15.
It's just insane how short games are, and it's all because of how easy it is to snowball a lead in Season 7. There is no such thing as "farm for late" in 2017 because of how the outcome of a game is already decided by 15 minutes. This meta is making this even worse with how much damage everything in the game deals. Something needs to change and it needs to change soon.