IME, there are 2 kinds of bad support players.
Support mains that don't understand how bottom/jungle/top/middle works so they don't know how best to support. These are the kind that down-voted my comment that I deleted I guess.
And autofilled supports that have zero intention of playing the game out normally and don't care if teammates suffer.
There are a lot of different kinds of good support players, but the bad ones still outnumber them.
Support mains usually have twisted ideas about what it means to be a support player, and autofilled supports read that crap and believe in it, so they repeat what they've been told. Not taking the time to learn the slot proves they don't care. Not all autofilled supports are bad though. A lot of them are just fine. I actually think it's less common for support mains to be decent. They still have that disconnect from not experiencing what it's like to play other slots well.
If I wasn't a fill main I'd get autofilled support a lot I guess, I don't really know, I'd rather do what I can to reduce the tensions within the team and minimize the chance someone gets autofilled. I'm sure I still get lots of autofilled players, but at least I'm trying to support the community by playing mainly fill.
To me, it would be easier if players that chose to fill were reassured with the knowledge that they couldn't get autofilled players on their team. I think people would be more often willing to fill if they knew they could get rewarded for it with such a precaution used for them.