Because league is based on math.
Offensive stats are a + vector, defensive stats are a - vector against the enemy + vector and utility stats are a multiplier for such vectors.
That being said, league is a game that has been transformed and shaped into pampering the widest audience possible, along with pushing a shady SJW propaganda.
While you're playing support you're basically like an amplfier, and the other 4 guys are the instruments attached to you.
Sure you can clean and mask the sound as much as you can, but in the end if who's playing the music is a complete incompetent moron or the instruments are very poor quality there isn't much you can do.
League is a game where we take it for granted that being dogshit it's completely fine, there are even people that think that plat elo is anything near acceptable, i even once had an argument with a D3 guy that thought that veigar is a viable support and athene's is a bad item on karma, this not only makes clear how unskilled you are at the game, but also how little you know about simple math.
Riot thinks it's ok to not know how to play the game and be a retard, because saying mean things it's far far worse, on the internet. (which has been unrightfully and forcefully occupied by corporations that made it their new marketplace at the expenses of whoever was there before them), so we're ended up with a game where it's basically like riding a tandem bicycle for 5 people where 4 people don't have legs, but if you point out the fact that they don't have legs you're basically satan.
My advice is, either be willing to suck all the scum soloQ is and have the patience to grind trough games, because if you're actually good it's just a matter of having time and patience to invest into the game (and the ability to not suffer brain damage when your teammates do the most dumb and irrational shit, which i lack greatly) or find someone you trust to duoQ with, because unless you're in high elo (D2+) playing support and expecting to win is basically masochistic self abuse, especially because even high elo most supports are actually low skill players that just got lucky and got carried their way into diamond.
Now, if i can add my 2 cents, no offense intended, you're probably not a good support as you might think you are, because support is a role that takes a long time and a lot of informations and learning to master, and a good support if he actually knows what he's doing can make the difference and most of the times a good support is way more impactful than the other roles.