@OP....
I think the space on the page for a particular ad is 'rented' and whether one clicks on them/ it to open doesn't matter. WP get paid some money regardless. Not sure though.
Probably the amounts of clicks to open is registered by those how placed the ad and if no one visits their site via WP they withdraw the ad probably. No attention, no opportunity to sell something, no income thus.
Again not sure, it's just my logic.