I am extremely slow at calling roles. Back when I started people didn't used to call their roles, it is weird to think there was a time like that but there was. Then the role calling thing caught on and I just didn't get into the habit of doing it.. as such I got put in support... and then I learnt to love it. I am most practiced at support than other roles so I am good at it.
I used to main support because I wanted an excuse to not be able to cs well
after 1 week of trying shit out, played Leona, stayed with Leona.. still playing Leona, will play Leona.
Because: Leona. 
I started playing support after seeing countless of bad supports.
Even thought i was Top/Mid main.. well I main support now.
I like to get carried
I'm kidding, it is well know that support play a major role and can be the difference between a win and a loss
I don't always main support, but when I do it's because I put it as my secondary.