Why do our teammates suck? Part QQ, part honest question, interested in YOUR opinion

First off, I'd like to point out that I don't claim I belong to higher elo or that my teammates are the only thing keeping me down or whatever. With some work this season I may just reach Gold, but this needs lotsa work on my part I guess. Consider the summoner's name ironic, for all intents and purposes.

Thus, as the nooblord all of you will brand me as, I gotta ask, why do our teammates sucks so much and so often. I am not talking about mechanical skill. This one fully depends on which champion you are playing, how much you've played with, whether you are lagging or not etc etc. But why do seemingly 80% of the player-base suck at decision making?

I admit, mechanically-wise, I've got ways to go. Vel'Koz and Wukong are the only champs I can trully say I am trully good with, eveyrthing else is, let's say average. But even with a champ I suck I rarely make such grandstanding mistakes as most people in my games seem to do.

Dragon isn't warded in advance, they start it with enemies around or go in to steal (?!) it AFTER the game has announced its fallen. Baron throws are a dime a dozen, no one waiting to see enemies on the bot side or bogged down in their base by supers. Toplaners rush into fights, trying to avenge themselves on an opponent who is already 2 items ahead, never waiting for the jungler's help. ADCs farm mid-ganks, supps try to force fights when their combo is bad at a certain level. Midlaners back into base instead of pushing or following the roamer. Junglers farm their camps when 2nd tier towers are falling or when we are trying to get one of theirs.

And no one seems to play for objectives. It's like everyone is looking for that one play for their YouTube montage when most of the time just sticking to boring old farming and warding to catch someone off guard is the easiest way to winning. People win teamfights, and 3 low-hp players prefer to go heal and play it safe (?!) during an ace instead of pushing. Tanks or hard-cc supps are scared to engage poke comps, letting them whittle their team down and "starting" the fight too late. Poke comps fight in jungle, all disorganized instead of sieging straight through a lane.

And the chasing! It's like 90% of the players have a hunter instinct overriding all their higher reasoning. And, of course, teammates join one after the other instead of pushing the other side of the map or something.

I've been playing this game on and off since mid-season 2, never bothered with ranked except this season. Due to long periods of ditching the game, my mechanics aren't all that cracked up and I don't claim to be that good. But come on! Every game I see people making mistakes that defy common sense. Mistakes that make me question how those people even make it to school/work without bumping into lampposts. I am honestly wondering WHY are people bad at an aspect of the game that is much easier to get and more intuitive than mechanics, cause it requires common sense and not MAD SKILLZ.

For the TL:DR guys: Why do players seem to have no KNOWLEDGE of this game? Everyone seems to be looking for DEH PLAYZ instead of staying safe and getting towers.