Support secondary before meant you get support pretty much all the time.
Additional backstory: I used to be jg/sup in season 5 before new champion select (didn't have to learn other roles, since I'd state my preference for jg, not always get it, but if I'm willing to sup, I would get that 99% of the time if I explain I'm jg/sup and ont much else. Under old system everyone had to support occasionally due to last pick, but if you had jg/sup, or any 3 roles including sup, you could stay with those and be OK).
In Season 6 though, I couldn't be jg/sup if I wanted to jungle most of the time, so switched to jg/mid. Thus LOL lost one sometimes-support player, I am sure there were many others.
I've been practicing a bunch of support since the new system :). I might still remain jg/mid (since I learned to mid pretty well at that time), but I'm willing to swtich with autofills at support, since I don't mind supporting, and am OK at it.
Corollary: if you got autofilled, ask if anyone wants to trade! People often will, and if you add "it's OK if not", i don't think many will take it the wrong way.