As a user I'm not going to allow your app to waste my limited data plan with ads, learn to cache them, or do something clever when the device is connected via wifi.
Maybe in the country you live the mobile internet is cheap and unmetered, but the appstore is international, if you don't want to deal with international users, you are free to lock your app by region. It's not your God-given right to use the user's data plan as you wish, even worse, in some countries you are going to waste your user's money in many orders of magnitude to perceive a cent (or less) for a banner.
If you are not going to care about your users, then don't complain about users not caring about your efforts.
You have the option to NOT use the app. You are not entitled to free ad-less apps created by other people's toil, anyway.