Why does everyone....

I think an easy way to fix OCD (obsessive carry disorder) if to reward people for things like assists. For example if a hero gets 10 assists the announcer could shout something like "Savior!" If someone gets 20 assists the announcer could shout "Guardian Angel!" Lastly if someone could scrape 30 assists in one game, it has only happened a handful of times for me, The announcer could proudly announce "Divine Intervention!". They could also have a counter on the top of the screen that counts the wards placed. Little things like that make life as a support worth wile.

1. It's worth pointing out that heroes with the carry role listed are almost evenly matched with all heroes who don't have the carry role listed (47 carries to 49 non-carries). That doesn't count heroes like Pudge and Nightstalker who are regularly played as carries. Even if your whole team randomed, it is statistically likely that you'd wind up with about 2-3 carries. By contrast, even including carries, there are only 28 support heroes (and only 12 primary support heroes) and 21 pushers (with a lot of overlap). It's a short-coming that will hopefully be remedied as Valve continues to release new heroes.

2. There's a generally sensible axiom about pugging in DOTA that I think I read here when I first started playing. "Play for the team; rely on yourself." Unfortunately, especially in the meta of low-level pug matches right now, relying on yourself as a support player is very difficult after the lane phase. You are probably under-geared (since you almost certainly had a carry in lane with you, bought the courier and maybe wards) and under-leveled against the enemy hero who was soloing mid and has come to gank you 3-2. So, you die while your carry partner hopefully escapes. You're even further behind on money and xp, and without actual competent help from your team, it will be very difficult to catch up, even if the team starts leading in total kills. You have to be present and alive to get rewards for those team fights, and you are low-hanging fruit for the enemy carries after a team-fight is initiated. Now you are being yelled at for your horrible K-D, even though you are playing Omni-Knight who is melee, has no real nukes, and because of his ulti is a prime target at the start of a fight. Sound familiar? Everyone who's pugged as a support in a low-ranked match has had this game, at least once, and it's enough to make you want to say, "Hell with these people. Let them buy their own courier and support themselves."

3. It's basic human psychology. All (or at least) most of the things people already said are true. People feel good about solid K-D ratios, they like to hear "Ultra Kill!" when it's them on the giving side of the kill, etc. Also, psychologically speaking, a support hero sounds like half a hero. He needs someone to support to be good, whereas a carry, once farmed, is by definition a complete package. Finally, lower-ranked players haven't got the game experience to plan for a fluid match (I certainly don't, and I feel like I'm doing well for being new). So, you tend to plan for not exactly best case scenario. You reasonably envision a few set-backs, a successful gank, some good early harass, etc. You don't plan for the enemy team to ward your jungle while you're farming on Ursa and to then come gank you while you're at half life engaged with a creep camp. So, the major drawback of a carry (that you have to farm consistently for longer than any non-carry) to reach your amazing potential doesn't really enter into their equations.

4. Carries are often (certainly not always) simpler characters to play. Think over the popular carries you see in low-ranked games (Drow, Sniper, Bloodseeker, Luna, etc.) All of these heroes have 2 passives. You only have to manage two buttons. I can't think of a single support hero with 2 passives; most don't even have 1. This appeals to a newer player who's micro, timing, and targeting are suspect.

5. Lastly, it's the sub-meta of low-ranked games. As far as I can tell watching replays of more skilled games, skilled games aren't really about who won more team fights or had the highest kill count. It's more like hockey. How well did you capitalize on the power-play where one or more opponents are in the penalty box (waiting to respawn). Lower-skilled games, especially pugs, don't have the coordination to do that most of the time. If they win a team fight and knock out 2 of the enemies, they don't form up and push mid and take a tower or barracks. They dither around looking for the other 3. So, the game actually is usually (slowly) decided by who team-fights better, more evenly distributes not only their deaths, but who kills them and gains the upper hand in xp and gold until that advantage is so big that they sweep in and win. I often see games go another twenty minutes after it's perfectly clear to me that the other team has won. It's 53 to 18, why are we all still here? Sometimes they're running up the score, but I feel like it's more often that they don't feel confident, even with a lead that size, that they can go in and get the win.