game times

So I've noticed a regular pattern of exceedingly short game times. The past few seasons you would regularly see games going past the 40 minute mark. but just now we saw a pro game finished out in 21 minutes in giants vs g2. most games finish in 30 minutes at the most and i havent had an hour long game all season. What is the cause for the shortened game time this season? is it a tower nerf I didnt notice? strengthening of minions? overall ad boost to champ? i dont think it can be the changes to rift herald as I'm low elo enough that very few rift heralds are even grabbed.