Safari/iOS adblockers need to use a specific Safari content blocking format which is different from the classic ABP format. Presumably the extra work to support this format (and the content blocking extension API) discourages some vendors.

Notifications are required as it is the only way to notify the app, and users, when we release updates to our ad blocking rules. Otherwise we would need to release an app update every time a blocking rule needs to change. We update the ad blocking rules generally weekly.