Ad networks haven't supported HTTPS fully on the web either, not just iOS. In fact, Google says you will earn less with just HTTP
"If you do decide to convert your HTTP site to HTTPS, please be aware that because we remove non-SSL compliant ads from the auction, thereby reducing auction pressure, ads on your HTTPS pages might earn less than those on your HTTP pages." [0]
I wouldn't be surprised if many app developers put in this exception because at the end of the day, they will hurt too if ads stop showing up.
"If you do decide to convert your HTTP site to HTTPS, please be aware that because we remove non-SSL compliant ads from the auction, thereby reducing auction pressure, ads on your HTTPS pages might earn less than those on your HTTP pages." [0]
I wouldn't be surprised if many app developers put in this exception because at the end of the day, they will hurt too if ads stop showing up.
[0] https://support.google.com/adsense/answer/10528?hl=en