It isn't about which team fed more. It isn't about who didn't group for a teamfight. It's about objectives. It's about what you don't collectively have, as a team. It's what you don't do, collectively as a team. It's about how hellbound determined all of you are in going out of your way to screw over your own team in order to benefit yourself, no matter how high the cost or short term the benefits are.
All the pentakills in the universe do not win the game. Objectives do. Destroying the enemy Nexus is the only winning criteria.
Everyone only wants to play assassins and ADCs these days, and most of them aren't even halfway beginning to slightly decent at it. A team of assassins and ADCs can only do one thing, and if they can't do it, then they are basically worthless, doubly so since nobody wants to focus on pushing objectives and especially not defend their own lanes. Hell, most of the time, nobody is able to even build up the gumption to see even halfway through to the end of the laning phase; the first chance they get, they fuck off to retire to the jungle or attempt to teamfight the enemy in the enemy jungle. They just go all in trying to get all the pentakills as soon as possible, and the instant that doesn't work, just give up on the game.
Nobody has crowd control; they just expect to one shot the entire enemy team no matter who they are at any time, regardless of context. They don't get armor penetration to deal with tanks or Grievous Wounds to deal with healers; they all equally expect to be able to outdamage Soraka's healing, and it never fucking works no matter how many times they try it and no matter how many times I warn them.
Nobody goes for any of the dragons, not even Infernal, which is the only one anyone ever cares about. Hell, I've had people tell me that getting Cloud dragon is a literal automatic loss, even though it boosts movement speed and they waste most of their time just trying to chase the enemy team, even through all the slows and stuns that get thrown their way.
Nobody wants to deal with vision control and instead foists all of that responsibility onto the support, which is the dumping ground role for everything that doesn't have anything to do with pentakills these days. Not by Riot, but the community. This leads to situations more often than not where the support will get targeted first, last and only because their death means the entire team collapses because they're the only one role actually doing anything, and that includes doing the same one single job that the entire community wants to focus on to the absolute exclusion of everything else.
Nobody wants to figure out why they keep losing against one champion or another. They just say that X champion is broken and too overpowered, and that it has nothing to do with them being stupid or not figuring out how to not get killed by one champion or another. In one game, I had my ADC flip their shit and just run down bot lane because Jinx was the enemy, and hyperfed her to "prove" their point that she was too overpowered.
And then all of you have the balls to come on here and bitch about game imbalance, when 99.999999999% of ALL the imbalance in the game is caused exclusively by your own terrible life decisions. And Riot is too goddamn nice to say that you constantly do this shit, and have been to an increasing degree over the years. They instead try to create team building systems that miserably fail within a few months of release because you use it as an excuse each time to overspecialize even further while delegating the support role to an unspecified fifth party member, which ends up being increasingly rarer with each passing day.
So next time you want to bitch about game imbalance, take a look in the mirror, because what you will see I guarantee is having many thousands of times more of an effect on the game's imbalance than anything that Riot has ever done, especially when they constantly patch the game TO try and balance it.