Some of the possible reasons are:

1. The tracker does not provide publisher granularity.
2. The tracker uses a different publisher field than the one you used in your query. Different trackers and ad networks identify publishers in different ways, and Singular uses three fields to contain this data - Publisher ID, Publisher Site ID, and Publisher Site Name. 
3. The ad network provides publisher granularity, i.e. actual cost per publisher, and therefore there is no need for an estimation.

Ideally, in such cases, your Singular report would display both the installs and the actual cost for each publisher. However, the publisher identifier pulled from the ad network may not match the publisher identifier pulled from the tracker. In that case, Singular cannot match the publisher and your Singular report shows them in different rows:

Singular analytics reports will sometimes display estimated stats in addition to the actual numbers pulled from various sources.

Estimated metrics are added when the data Singular pulls from ad networks is not available in the same granularity as data from the attribution provider (tracker). In order to help you optimize your campaigns, Singular interpolates numbers for the ad network metrics in the finer granularity. 

In the example below, Singular calculates an estimated cost per publisher by dividing the overall cost between the publishers in the same proportions as the installs. 

The process is currently used to estimate cost (and other network metrics) per publisher and country when the network data isn't already broken down.

In order to help you optimize your campaigns, we always try to provide the data broken down by country.

1. When ad networks and other sources provide country granularity, Singular shows it.
2. When ad networks do not provide country information, Singular tries to provide this granularity anyway by looking at the targeting settings in the network and/or the tracker data for the same campaign (if we have it):
   • If the campaign, sub-campaign, or creative is targeted at one country, we'll show that country in the report.
   • If there are multiple countries targeted, and we also have tracker data for the same campaign, we'll try to estimate the cost per country by dividing the overall cost between the countries in the same proportions as the installs (see example below).

Singular applies the following logic to decide whether to calculate estimated metrics:

1. The ad network data is compared with tracker data based on the day, app, and source, as well as campaign (if campaign granularity is available).
2. If the data in the ad network is already broken down by publisher, Singular does not add estimated metrics as they are not needed.
3. If the data in the ad network is not broken down by publisher, but the tracker data does include that granularity, Singular tries to provide the missing granularity by estimating cost per publisher.