Fill = Support, or What I've learned by default maining support.
There is an issue with the queue at the moment, but that isn't what I am mainly here to talk about.
To get it out of the way, an issue with the queue at the moment is that it doesn't matter what you select as your main, you are nearly guaranteed to get support if you select fill as the second position. If you select fill as the first position, you will almost certainly get support.
I selected fill as the main role and after I noticed a trend I started counting. By the 12th time (after I began to count) I had selected it, I had gotten support 11 times, but the twelfth time I got top. Before the game started someone didn't lock in and so I was sent back to queue where I again got support. Last night, after 24/25 times being matched as a support I actually made it in game as an ADC. Something isn't right about that.
After playing 30-40 of my last 35-40 matches as support, I feel that I have learned a few things about support, and why that role is persistently at the bottom of the desired positions to play.
It can be boring. As a support you are expected to, if all goes OK, sit there and let your partner farm. In a public queue, especially solo, you really can't reliably do much more than that. If you initiate and your partner isn't reactive enough then you can get killed, or worse they can be killed. If you have good synergy in a public game you could randomly do well, but most of the time your ADC didn't select ADC as their primary position either and if they lag at all then you are more than likely often going to just get killed or get them killed. So, unfortunately your role is actually to be reactive instead of proactive. You are supposed to wait until there is an opening and then just hope to god that your lane partner is ready to react to that opening with you. Even if you are a healer, you are still limited to reacting to the other teams attempts to get an opening. It makes the first 20 minutes of a game a lethargic round of cat and mouse.
There are very few reliably consistently loved supports. I haven't just been playing as support, I have been playing against them too. Common supports that every ADC is cool with include: Taric, Alistar, Soraka, Sona, Leona. (More on blitz and thresh in a minute) Of those, the ones that really seem to be preferred are Sona, Taric, Alistar. These really have not changed much, and the key point to all of them is healing, a reactive skill that you have to be on top of as they might be the primary benefit your ADC considers, but it is definitely the one that they will notice the most if you are not consistently doing it. Again, this is simply reactive. The skills that make these champions "preferred" are their stuns/knock-ups. Even if you have a Malphite playing support, your ADC doesn't really love you until you are level 6. The only supports people seem to love before level 6 are the healers, and of the healing capable you are left with Sona, Taric, and Alistar being the favorites because they have crowd control and healing. The only time another support seems to be popular is when they are in desperate need of a nerf, but the consistently preferred supports are those three. There are supports who are played more often, but those three are the ones that any ADC would love to have in lane with them.
Get to the kitchen and make me a sandwich, a.k.a know your role. As a support you are not supposed to kill anything. Ever. You see that minion in lane? Don't touch it. You see that champion that you can kill? Unless every single member of your team is no where near that easily kill-able champion or they are literally unable to land a shot, a support is not to kill an enemy champion. Ever. Most of your team views that a support with more than 5 kills is a bad thing, and your assists are only considered by the community to be a half kill. There is no praise or reward for your assists in a game. No one will ever say, "Man, your 25+ assists are why we won the game." If you and your partner dive, your ADC dies, and you get the kill instead of him, after they match people will just say you got clean up kills. Your job is to be passive and react to what your partner needs, and only initiate if the opportunity arises. If you have a CS score by minute 10 over 10, your ADC is probably mad at you. Being told to stay in the kitchen and make your ADC a sandwich isn't fun. Looking at some statistics, your highest win rate supports average less than 3 kills, less than 6 deaths, less than 15 assists and less than 25 cs. In a 30 minute game you get to kill less than one thing a minute. (Including creeps) A "good" support has a 0.5 KD unless you include assists as half, and then they have ~1.6. Just a reminder though, no one really cares or praises you about your assists, so your KD is 0.5.
The CC supports rely on your ADC too much It is virtually impossibly to play a CC support well unless your ADC is not only familiar with the champion they are playing, but you and they must also also have a decent internet connection. Not too long ago, riot released "Ping, Winrate, and Vayne Probs" which was a study of how ping effects a players win rate. Support was a full median rank 20 points below that of jungle's. The role most necessary to have a good internet connection was ADC. In short, because this post is already long, if your ADC cannot capitalize on you getting a pull with Blitzcrank or Thresh, or a stun with Taric, or a knock up with Nami, then it doesn't matter how well you play your support role because you won't make enough of a trade to offset the damage the two of them can do to you. If you are a CC support and playing against a healer you are better off not even trying to poke. If you are playing with some one you do not know, then this situation can be risky at best, and at worst you are simply gambling every time you try to make a pull or land a poke because you are not sure if your partner can capitalize on the move or position their champion to keep the other team's bot from diving on you.
Everyone has wards, but it is still your job to ward. If you are not there for a fight involving more than 2 people, everyone hates you. If you are not warding jungle where none of your team is, everyone hates you. If you get killed while trying to ward, everyone hates you. Despite everyone having wards, you are the only one responsible for warding.
TL;DR
In queue, fill = support.
Support is not a fun role to play because it requires you to be passive and reactive, not proactive.
A successful support requires the ADC to have a good connection and for them to be ready and able to react.
Only your can prevent jungle fires. Warding