The iAd App Network will be discontinued as of June 30, 2016. Although we are no longer accepting new apps into the network, advertising campaigns may continue to run and you can still earn advertising revenue until June 30.
Scott Forstall was the biggest advocate of iAd amongst Apple’s leadership.
With that tidbit in mind, I'm a little surprised it took this long for them to pull the plug.
After Forstall, I don’t think anyone was really interested in iAd at Apple and it was more of an afterthought, so it makes sense to kill it finally.