Apparently it's a performance issue. From apple[1]: Note: Apps containing content blocking extensions for Safari on iOS are available only on 64-bit devices, d

Apparently it's a performance issue. From apple[1]: Note: Apps containing content blocking extensions for Safari on iOS are available only on 64-bit devices, due to performance limitations of 32-bit devices. [1]: https://developer.apple.com/library/prerelease/ios/releasenotes/General/WhatsNewInSafari/Articles/Safari_9.html#//apple_ref/doc/uid/TP40014305-CH9-SW9