I just came from a match where a gragas(Support) Refused to build redemption even though it would help us massively in team fights.
He tells me to build it as "He know what he is doing"
I told him that i couldnt sacrifice anymore tankiness to build it as i was the only tank on the team and i was getting melted with in 0.5 seconds.
Like shit man, i'm asking you to build an item not sacrifice your cat to teemo.
Atleast he responded, I asked my 
top to build 
as he was losing to a 
....both times I roamed top as a 
support ..to bail him out and we both killed nasus both times...and both times I ask him to build black cleaver so I wont have to come up again....he just builds 
c: c: c: against an armor stacking .... c: c: c: c:
The Following reasons:
Pride.
Ego.
Omnipotence.
Arrogant.
Hard Headed.
Draaaaven.
Take your pick.
Probably because of how you ask.
There are different ways of asking someone to do something.
Are you being polite and respectful when suggesting certain item builds? Or are you being rude and condescending?
Not everyone is going to take you on your word about how helpful an item might be. Sometimes they just don't understand, and you don't have the time in a game to explain it to them either.
telling junglers (especially the ones going full ad and feeding) to go tank is the 2nd hardest thing to do in this game.
the first being telling low elo players to ward
When i address some players as retards i'm no liar. Yet truth is considered inconvenient so (always said retards) have come up with a new term to cover it: toxic.
Stupidity, nothing else, people so weak and dumb that they're too coward that they even run from themselves.
like when an adc complains about a tank being unkillable and doesn't build 
or 
This would be different if it was like Miss Fortune building Randuin's Omen, or Amumu building Bloodthirster, and you were telling them that they don't synergize with those items. But this is Redemption, which everyone seems to think is 100% necessary on supports.
is not always necessary on supports. There are legit wasted stats on the thing if you do not already sport a heal or a shield, so asking a Gragas to build it is ludicrous. Gragas should be building things like Iceborn Gauntlet, Rylai's, Face of the Mountain, and a few other things that compliment his play style as a beefy mage-tank. While Redemption does have some universal stats, it doesn't flow with Gragas' play style. If you recommended he build the Proto-Belt, yeah, that would fit. But seriously, Redemption isn't core on every support, so get over it.
bc they dont want someone telling them what to do they already have that irl simple as that no ands ifs or buts about
He tells me to build it as "He know what he is doing"
You answered your own question. Unfortunately, a lot of players don't know what they're doing and just imitate things they've seen before by other players/streamers/pro players and think that is enough to perform. They don't consider WHY those players went certain builds at certain items and so on. A Support Gragas should generally build Redemption, though... Cooldown, Mana Regen, Healing, bonus HP, all stuff he kind of needs.
