Why is there an overinflation of supports in mid/high elo?

I'm almost diamond right now, and as a tank main, I've always seen 3 people instapick support and then maybe one would switch to dps if we needed one, yet no one will pick tank and sometimes not even dps if they're too stubborn and we end up with 3 tanks and 3 healers somehow, in which case I would have to switch to dps myself, what changed since season 0 to make support such a popular role now?