Many advertisers like to get performance data on an app or site before they start filling lots of ad opportunities from it. Most advertisers monitor the view through rate/completion rate (VTR) and click through rate (CTR) of their campaigns on each property, and when properties do not perform up to their standards they stop sending filled ads to them. Advertisers do not have any of this data on new sites so they will only fill a small amount of the ad requests sent to them until they learn how the traffic performs. If the traffic performs well than the advertiser will most likely fill more ad requests in the future and will be more willing to pay higher CPMs.
Another hindrance for new sites and apps is that many advertisers must approve them before they will start filling their ad requests. The approval process allows the advertiser to review the property to ensure it meets their quality standards. This also allows advertisers to know where their ads are being displayed.
Once a new site or app has been approved then optimization must be done to ensure that the best performing advertisers are given first shot to fill the ad request and that there are proper call backs and fail overs to make sure all advertisers have a shot at filling the ad request before it ends up unfilled.
The optimization process is continual and will always be happening in order to maximize revenue, but until the advertisers are able to gather data on new properties and it has received all approvals the optimization process is limited. The number of ad requests sent from the property can also impact how long it takes advertisers to gather sufficient data to determine if they like the traffic or not.
Some publishers can be very impatient and if they do not see high fill rates and/or high CPMs within the first week they want to move on to the next advertiser or advertising exchange. This can stunt the process and may require it to start all over again.
A reasonable amount of time must be allowed for the new property to be approved and analyzed by the advertisers and then time allowed for the optimization process. The time frame can vary but if the fill rate is still very low after 2 months than either the traffic is not performing for the advertiser(s) or the optimization process is failing and it may be time to try another ad exchange.