Some people don't realize there aren't only ganking mids, and even if it's a ganking mid hero, they expect what you said. They're dying in their lanes and then they go "mid ???????? where are u?????". I'm not fucking responsible if you die with Bristle in offlane (how can anyone die with bristle in duo offlane with no stuns?)
Yes, if there were only ganking mids and the mid player "had" to gank nonstop, then the best new strat would be to play your #1 hard carry mid and let him freefarm 24/7 while his opponent is absent.
And there is a huge difference between "hey mid, not doing so good up here could you help up with a gank we can set up with some harassment and then a stun" and "OMG MID FUCK U NOOB NO GANK GG NOOB"
Also, the whole "mid is ganker" thing is just a relic left over from olden times, like many other things. People never stop to think about it or question it, they just automatically call anyone going against the "everyone knows it" facts a noob. Mid is a worse lane to gank from than top and bottom.