See, here's the thing. You want to prolong the games with this change, which I agree would be better.
The problem is that Riot DOESN'T want longer games. Look at the changes introduced this off season:
- Possibility of getting 2 rift heralds, which can help take out more turrets faster, and thus end the game faster
- Dragon Soul, which gives a huge power spike to the entire team that get's it, helping them to close out the game
- Elder Dragon, which is just flat out bullshit in its execute function and causes the team with it to have a massive advantage in team fights to, guess what, finish games off... and also crowds out champions who are SUPPOSED to want to fight at lower health values, like Olaf for example, but that's just a problem of shortsightedness Riot's part
They literally just added a bunch of additional "objectives" to the game that help end the game faster. Baron was already a huge advantage for the team that get's it, since they basically get to push each lane with impunity and the other team can't push back. Now you've got even more power that can just straight up end the game, and before anyone tries to say that Dragon Soul or Elder Dragon are "late game objectives", no, they aren't. They can be claimed before the 30 minute mark, and make comebacks even harder to achieve than they already were in Riot's enforced snowball meta.
Now yes, obviously none of those additions just automatically end the game when someone gets them, but the team who is ahead when they become available has a huge advantage in claiming them, which favors snowballing.
The BEST change they made this pre-season? Well, actually it was removing
... but the NEXT best change this pre-season was turret plates giving less gold. Now, personally, I think turret plates should give NO gold at all, and should simply exist to make taking turrets harder in the early portion of the game. But then again, that's because I think the lane pressure and wave control of taking a turret is reward enough for claiming that "objective"
tl;dr - Riot wants games to end faster, which is easily proven by how many additional rewards there are to be had for the team that get's a lead. As if having more items and more levels for more base stats wasn't enough of an advantage.