It is possible that some apps are not ranked for keywords at all. In this case, you have to start with checking your app text metadata.
- If you find that the reason why you are not ranked for keywords is in your text content you have to optimize your app title, short and long description on Google Play or title, subtitle and keywords field on AppStore.
- If your metadata contains keywords that you would like to be ranked for you can try to set a CPI campaign which may help to get into the index.
